In Zapier, set up a webhooks trigger and configure it to send a POST request to your customer salesforce API endpoint. You’ll need to authenticate the request by including an authorization header or API key, depending on how your customer API is set up for authentication. Consult Salesforce API documentation for the specific authentication requirements. 

Put https:// + your SF domain + /service API call into the field. When I first used this, I assumed that the API already knew the SF domain from the connection, but it does not. It wants the full URL.

Custom APIs are similar to the standard one which are referred in the document. but looks like Zapier is doing HTTP call and salesforce is expecting HTTPS

Hi @narendraadhikari!

I’m not super familiar with custom APIs in Salesforce, versus using their standard ones that are documented.

Are there API reference docs available for that? Something like this, for example: https://developer.salesforce.com/docs/atlas.en-us.api_rest.meta/api_rest/resources_list.htm

The API Request action is an advanced one that uses your existing authentication (super helpful compared to using Webhooks), but in order to help troubleshoot what to put there, it would be great if you have any reference docs for what the API is expecting :)