Getting Error "We hit an error adding your new account"

I am going to publish zapier custom integration.

Using API Authentication, I tried to setup my endpoint url to accept the api key generated by my backend.

I have tested it on POSTMAN, and it was working well. But when I was trying to test authentication on zapier integration, it is displaying “We hit an error adding your new account in zapier”


authentication failed: The app returned "503". What happened (You are seeing this because you are an admin): Stack trace: ResponseError: {"status":503,"headers":{"content-type":"text/html; charset=UTF-8","retry-after":null},"content":"<!DOCTYPE HTML>\n<html lang=\"en-US\">\n<head>\n <meta http-equiv=\"X-UA-Compatible\" content=\"IE=Edge\" />\n <meta name=\"robots\" content=\"noindex, nofollow\" />\n <meta name=\"viewport\…" 

So this does not allow me to test any triggers and actions.
I am not sure what the problem is. 
Do I need to upgrade my plan to create the zapier integration? 
Please let me know if you have any ideas.
Thank you.

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