Hi @CrishThome - I’m sorry that you’re having some trouble setting up a private Zapier integration. I can see that you’ve been in touch with the Support Team about this. I’m going to share  part of their reply here in case it helps anyone having a similar issue:

The easiest way to get a Zapier integration up and running is to setup webhooks on your side that can be configured by the user and sent to Zapier.

Elementor is a good example of how this works: https://docs.elementor.com/article/263-zapier

Where the user setups up a form in Elementor and as part of that they can put in a Webhook URL for the data to be sent to.

Then in Zapier the user can setup a Webhooks by Zapier Catch Hook trigger to to catch the hook every time that somebody fills out a Form in Elementor.

https://zapier.com/help/create/code-webhooks/trigger-zaps-from-webhooks

I'm not sure what is involved with setting that up on your end - but it might be easier that building a full REST API. And with that setup above - you wouldn't have to build a Zapier integration.

Have you confirmed using a tool like Postman that you are getting an error when using the wrong credentials? https://www.postman.com/products

Finally - these are some other resources I found that might be helpful.

https://zapier.com/developer/documentation/v2/integration-developers-partners/

https://rapidapi.com/blog/20-tutorials-on-how-to-create-your-own-api-sorted-by-programming-language/

But it seems like if you can do webhooks - that is the simplest solution.

If not - then it seems like the authentication on the API side is not setup correctly in some way as the API should return the error if the credentials are incorrect.