flowstudio-power-automate-debug

Power Automate Debugging with FlowStudio MCP

A step-by-step diagnostic process for investigating failing Power Automate cloud flows through the FlowStudio MCP server.

Real debugging examples: Expression error in child flow | Data entry, not a flow bug | Null value crashes child flow

Prerequisite: A FlowStudio MCP server must be reachable with a valid JWT. See the flowstudio-power-automate-mcp skill for connection setup.
Subscribe at https://mcp.flowstudio.app

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Source of Truth

Always call tools/list first to confirm available tool names and their parameter schemas. Tool names and parameters may change between server versions. This skill covers response shapes, behavioral notes, and diagnostic patterns — things tools/list cannot tell you. If this document disagrees with tools/list or a real API response, the API wins.

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Python Helper

import json, urllib.request

MCP_URL   = "https://mcp.flowstudio.app/mcp"
MCP_TOKEN = "<YOUR_JWT_TOKEN>"

def mcp(tool, **kwargs):
    payload = json.dumps({"jsonrpc": "2.0", "id": 1, "method": "tools/call",
                          "params": {"name": tool, "arguments": kwargs}}).encode()
    req = urllib.request.Request(MCP_URL, data=payload,
        headers={"x-api-key": MCP_TOKEN, "Content-Type": "application/json",
                 "User-Agent": "FlowStudio-MCP/1.0"})
    try:
        resp = urllib.request.urlopen(req, timeout=120)
    except urllib.error.HTTPError as e:
        body = e.read().decode("utf-8", errors="replace")
        raise RuntimeError(f"MCP HTTP {e.code}: {body[:200]}") from e
    raw = json.loads(resp.read())
    if "error" in raw:
        raise RuntimeError(f"MCP error: {json.dumps(raw['error'])}")
    return json.loads(raw["result"]["content"][0]["text"])

ENV = "<environment-id>"   # e.g. Default-xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx

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Step 1 — Locate the Flow

result = mcp("list_live_flows", environmentName=ENV)
# Returns a wrapper object: {mode, flows, totalCount, error}
target = next(f for f in result["flows"] if "My Flow Name" in f["displayName"])
FLOW_ID = target["id"]   # plain UUID — use directly as flowName
print(FLOW_ID)

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Step 2 — Find the Failing Run

runs = mcp("get_live_flow_runs", environmentName=ENV, flowName=FLOW_ID, top=5)
# Returns direct array (newest first):
# [{"name": "08584296068667933411438594643CU15",
#   "status": "Failed",
#   "startTime": "2026-02-25T06:13:38.6910688Z",
#   "endTime": "2026-02-25T06:15:24.1995008Z",
#   "triggerName": "manual",
#   "error": {"code": "ActionFailed", "message": "An action failed..."}},
#  {"name": "...", "status": "Succeeded", "error": null, ...}]

for r in runs:
    print(r["name"], r["status"], r["startTime"])

RUN_ID = next(r["name"] for r in runs if r["status"] == "Failed")

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Step 3 — Get the Top-Level Error

CRITICAL: get_live_flow_run_error tells you which action failed. get_live_flow_run_action_outputs tells you why. You must call BOTH. Never stop at the error alone — error codes like ActionFailed, NotSpecified, and InternalServerError are generic wrappers. The actual root cause (wrong field, null value, HTTP 500 body, stack trace) is only visible in the action's inputs and outputs.

err = mcp("get_live_flow_run_error",
    environmentName=ENV, flowName=FLOW_ID, runName=RUN_ID)
# Returns:
# {
#   "runName": "08584296068667933411438594643CU15",
#   "failedActions": [
#     {"actionName": "Apply_to_each_prepare_workers", "status": "Failed",
#      "error": {"code": "ActionFailed", "message": "An action failed..."},
#      "startTime": "...", "endTime": "..."},
#     {"actionName": "HTTP_find_AD_User_by_Name", "status": "Failed",
#      "code": "NotSpecified", "startTime": "...", "endTime": "..."}
#   ],
#   "allActions": [
#     {"actionName": "Apply_to_each", "status": "Skipped"},
#     {"actionName": "Compose_WeekEnd", "status": "Succeeded"},
#     ...
#   ]
# }

# failedActions is ordered outer-to-inner. The ROOT cause is the LAST entry:
root = err["failedActions"][-1]
print(f"Root action: {root['actionName']} → code: {root.get('code')}")

# allActions shows every action's status — useful for spotting what was Skipped
# See common-errors.md to decode the error code.

---

Step 4 — Inspect the Failing Action's Inputs and Outputs

This is the most important step. get_live_flow_run_error only gives you a generic error code. The actual error detail — HTTP status codes, response bodies, stack traces, null values — lives in the action's runtime inputs and outputs. Always inspect the failing action immediately after identifying it.

# Get the root failing action's full inputs and outputs
root_action = err["failedActions"][-1]["actionName"]
detail = mcp("get_live_flow_run_action_outputs",
    environmentName=ENV,
    flowName=FLOW_ID,
    runName=RUN_ID,
    actionName=root_action)

out = detail[0] if detail else {}
print(f"Action: {out.get('actionName')}")
print(f"Status: {out.get('status')}")

# For HTTP actions, the real error is in outputs.body
if isinstance(out.get("outputs"), dict):
    status_code = out["outputs"].get("statusCode")
    body = out["outputs"].get("body", {})
    print(f"HTTP {status_code}")
    print(json.dumps(body, indent=2)[:500])

    # Error bodies are often nested JSON strings — parse them
    if isinstance(body, dict) and "error" in body:
        err_detail = body["error"]
        if isinstance(err_detail, str):
            err_detail = json.loads(err_detail)
        print(f"Error: {err_detail.get('message', err_detail)}")

# For expression errors, the error is in the error field
if out.get("error"):
    print(f"Error: {out['error']}")

# Also check inputs — they show what expression/URL/body was used
if out.get("inputs"):
    print(f"Inputs: {json.dumps(out['inputs'], indent=2)[:500]}")

What the action outputs reveal (that error codes don't)

Error code from get_live_flow_run_error	What get_live_flow_run_action_outputs reveals
ActionFailed	Which nested action actually failed and its HTTP response
NotSpecified	The HTTP status code + response body with the real error
InternalServerError	The server's error message, stack trace, or API error JSON
InvalidTemplate	The exact expression that failed and the null/wrong-type value
BadRequest	The request body that was sent and why the server rejected it

Example: HTTP action returning 500

Error code: "InternalServerError" ← this tells you nothing

Action outputs reveal:
  HTTP 500
  body: {"error": "Cannot read properties of undefined (reading 'toLowerCase')
    at getClientParamsFromConnectionString (storage.js:20)"}
  ← THIS tells you the Azure Function crashed because a connection string is undefined

Example: Expression error on null

Error code: "BadRequest" ← generic

Action outputs reveal:
  inputs: "body('HTTP_GetTokenFromStore')?['token']?['access_token']"
  outputs: ""   ← empty string, the path resolved to null
  ← THIS tells you the response shape changed — token is at body.access_token, not body.token.access_token

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Step 5 — Read the Flow Definition

defn = mcp("get_live_flow", environmentName=ENV, flowName=FLOW_ID)
actions = defn["properties"]["definition"]["actions"]
print(list(actions.keys()))

Find the failing action in the definition. Inspect its inputs expression to understand what data it expects.

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Step 6 — Walk Back from the Failure

When the failing action's inputs reference upstream actions, inspect those too. Walk backward through the chain until you find the source of the bad data:

# Inspect multiple actions leading up to the failure
for action_name in [root_action, "Compose_WeekEnd", "HTTP_Get_Data"]:
    result = mcp("get_live_flow_run_action_outputs",
        environmentName=ENV,
        flowName=FLOW_ID,
        runName=RUN_ID,
        actionName=action_name)
    out = result[0] if result else {}
    print(f"\n--- {action_name} ({out.get('status')}) ---")
    print(f"Inputs:  {json.dumps(out.get('inputs', ''), indent=2)[:300]}")
    print(f"Outputs: {json.dumps(out.get('outputs', ''), indent=2)[:300]}")

⚠️ Output payloads from array-processing actions can be very large. Always slice (e.g. [:500]) before printing.

Tip: Omit actionName to get ALL actions in a single call. This returns every action's inputs/outputs — useful when you're not sure which upstream action produced the bad data. But use 120s+ timeout as the response can be very large.

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Step 7 — Pinpoint the Root Cause

Expression Errors (e.g. split on null)

If the error mentions InvalidTemplate or a function name:

1. Find the action in the definition
2. Check what upstream action/expression it reads
3. Inspect that upstream action's output for null / missing fields

# Example: action uses split(item()?['Name'], ' ')
# → null Name in the source data
result = mcp("get_live_flow_run_action_outputs", ..., actionName="Compose_Names")
if not result:
    print("No outputs returned for Compose_Names")
    names = []
else:
    names = result[0].get("outputs", {}).get("body") or []
nulls = [x for x in names if x.get("Name") is None]
print(f"{len(nulls)} records with null Name")

Wrong Field Path

Expression triggerBody()?['fieldName'] returns null → fieldName is wrong. Inspect the trigger output to see the actual field names:

result = mcp("get_live_flow_run_action_outputs", ..., actionName="<trigger-action-name>")
print(json.dumps(result[0].get("outputs"), indent=2)[:500])

HTTP Actions Returning Errors

The error code says InternalServerError or NotSpecified — always inspect the action outputs to get the actual HTTP status and response body:

result = mcp("get_live_flow_run_action_outputs", ..., actionName="HTTP_Get_Data")
out = result[0]
print(f"HTTP {out['outputs']['statusCode']}")
print(json.dumps(out['outputs']['body'], indent=2)[:500])

Connection / Auth Failures

Look for ConnectionAuthorizationFailed — the connection owner must match the service account running the flow. Cannot fix via API; fix in PA designer.

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Step 8 — Apply the Fix

For expression/data issues:

defn = mcp("get_live_flow", environmentName=ENV, flowName=FLOW_ID)
acts = defn["properties"]["definition"]["actions"]

# Example: fix split on potentially-null Name
acts["Compose_Names"]["inputs"] = \
    "@coalesce(item()?['Name'], 'Unknown')"

conn_refs = defn["properties"]["connectionReferences"]
result = mcp("update_live_flow",
    environmentName=ENV,
    flowName=FLOW_ID,
    definition=defn["properties"]["definition"],
    connectionReferences=conn_refs)

print(result.get("error"))  # None = success

⚠️ update_live_flow always returns an error key. A value of null (Python None) means success.

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Step 9 — Verify the Fix

Use resubmit_live_flow_run to test ANY flow — not just HTTP triggers. resubmit_live_flow_run replays a previous run using its original trigger payload. This works for every trigger type: Recurrence, SharePoint "When an item is created", connector webhooks, Button triggers, and HTTP triggers. You do NOT need to ask the user to manually trigger the flow or wait for the next scheduled run.

The only case where resubmit is not available is a brand-new flow that has never run — it has no prior run to replay.

# Resubmit the failed run — works for ANY trigger type
resubmit = mcp("resubmit_live_flow_run",
    environmentName=ENV, flowName=FLOW_ID, runName=RUN_ID)
print(resubmit)   # {"resubmitted": true, "triggerName": "..."}

# Wait ~30 s then check
import time; time.sleep(30)
new_runs = mcp("get_live_flow_runs", environmentName=ENV, flowName=FLOW_ID, top=3)
print(new_runs[0]["status"])   # Succeeded = done

When to use resubmit vs trigger

Scenario	Use	Why
Testing a fix on any flow	resubmit_live_flow_run	Replays the exact trigger payload that caused the failure — best way to verify
Recurrence / scheduled flow	resubmit_live_flow_run	Cannot be triggered on demand any other way
SharePoint / connector trigger	resubmit_live_flow_run	Cannot be triggered without creating a real SP item
HTTP trigger with custom test payload	trigger_live_flow	When you need to send different data than the original run
Brand-new flow, never run	trigger_live_flow (HTTP only)	No prior run exists to resubmit

Testing HTTP-Triggered Flows with custom payloads

For flows with a Request (HTTP) trigger, use trigger_live_flow when you need to send a different payload than the original run:

# First inspect what the trigger expects
schema = mcp("get_live_flow_http_schema",
    environmentName=ENV, flowName=FLOW_ID)
print("Expected body schema:", schema.get("requestSchema"))
print("Response schemas:", schema.get("responseSchemas"))

# Trigger with a test payload
result = mcp("trigger_live_flow",
    environmentName=ENV,
    flowName=FLOW_ID,
    body={"name": "Test User", "value": 42})
print(f"Status: {result['responseStatus']}, Body: {result.get('responseBody')}")

trigger_live_flow handles AAD-authenticated triggers automatically. Only works for flows with a Request (HTTP) trigger type.

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Quick-Reference Diagnostic Decision Tree

Symptom	First Tool	Then ALWAYS Call	What to Look For
Flow shows as Failed	get_live_flow_run_error	get_live_flow_run_action_outputs on the failing action	HTTP status + response body in outputs
Error code is generic (ActionFailed, NotSpecified)	—	get_live_flow_run_action_outputs	The outputs.body contains the real error message, stack trace, or API error
HTTP action returns 500	—	get_live_flow_run_action_outputs	outputs.statusCode + outputs.body with server error detail
Expression crash	—	get_live_flow_run_action_outputs on prior action	null / wrong-type fields in output body
Flow never starts	get_live_flow	—	check properties.state = "Started"
Action returns wrong data	get_live_flow_run_action_outputs	—	actual output body vs expected
Fix applied but still fails	get_live_flow_runs after resubmit	—	new run status field

Rule: never diagnose from error codes alone. get_live_flow_run_error identifies the failing action. get_live_flow_run_action_outputs reveals the actual cause. Always call both.

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Reference Files

• common-errors.md — Error codes, likely causes, and fixes
• debug-workflow.md — Full decision tree for complex failures

Related Skills

• flowstudio-power-automate-mcp — Core connection setup and operation reference
• flowstudio-power-automate-build — Build and deploy new flows