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Power Platform Community / Forums / Power Apps - Connector Development / Expected array, got st...
Power Apps - Connector Development
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Expected array, got string error in Power Platform Custom Connector

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Posted on 8 Apr 2025 15:46:44 by AS-08041537-0 4

Hi everyone,
I am building a Custom Connector in Power Platform for my pharma inventory MCP API. It is powered by a Node.js Express server exposed via ngrok and defined using Swagger 2.0.
I have two endpoints:
POST /invoke – works as expected
GET /tools – throws an error only inside the connector test tab
"Property "" type mismatch, Expected: "array", Actual: "string""However, when I test the same GET /tools endpoint using a browser, Postman, or curl, it correctly returns a JSON array. The server sets the Content-Type to application/json, and the Swagger spec defines the response as type: array with items of type: object.
I have already tried the following:
Set the Accept: application/json header in the Swagger definition
Restarted ngrok and updated the Swagger host accordingly
Verified that the response from the server is not HTML or a string
Still, Power Platform interprets the response incorrectly.
Has anyone else experienced this with custom connectors? How can I ensure Power Platform reads the JSON array correctly from a GET endpoint?
Thanks
Aditya Sinha
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  • AS-08041537-0 Profile Picture
    AS-08041537-0 4 on 09 Apr 2025 at 15:10:47
    Expected array, got string error in Power Platform Custom Connector
    @MichaelFP the swagger or yml is as expected and the output is correct when i go the ngrok url or localhost. Just that when i test it in my custom connector, it defaults back to the ngrok html page.
  • AS-08041537-0 Profile Picture
    AS-08041537-0 4 on 09 Apr 2025 at 15:08:06
    Expected array, got string error in Power Platform Custom Connector
    @MS.Ragavendar the postman responses are as expected.
  • MS.Ragavendar Profile Picture
    MS.Ragavendar 1,659 on 09 Apr 2025 at 13:13:34
    Expected array, got string error in Power Platform Custom Connector
     
    Did u test the endpoint with the postman, what is the output in the postman.
  • MichaelFP Profile Picture
    MichaelFP 1,831 Super User 2025 Season 1 on 09 Apr 2025 at 12:00:37
    Expected array, got string error in Power Platform Custom Connector
    when you see the swagger in the custom connector, what show to you in the response?

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