Unsure which url to use when authorising Apps to use Mautic

Your software
My Mautic version is: 2.16.2
My PHP version is: 7.1.33

Your problem
My problem is: I am trying to connect Mautic with other Apps and am unsure how to do this.

I am trying to hook up Calendy with my Mautic instance.
I am a bit confused about how to authorise an App to use Mautic and which url to specify in the authorization request.

These errors are showing in the log:

When i try and authorize Calendy through the Postman App with the following request i get a 200 return and the Mautic login in the Postman body reply, which does not do anything when i click submit.


Then i tried the same directly through the browser:

Uh oh! I think I broke it. If I do it again, please report me to the system administrator!

500 Internal Server Error

Steps I have tried to fix the problem:

I have tested my Calendy app with hook bin.com and it works well.

From Calendy documentation (https://developer.calendly.com/docs/webhook-subscriptions)

Please close this ticket.
I have discovered the api tester which should do what i need.