This is an Internal 500 error which occurs when server cannot process the request for an unknown reason.
Can you try out a few things. Try to send this request from Postman first. If the request goes through, then you can export the request in Postman Collection (Make sure this is imported as v1). Now, you can import the collection and the custom connector will be created for you.
If you can share more details about the API that you are trying to call along with the required authentication method, then we might be able to help you better.
Hope this Helps!
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