New Function API Key Header

Before the 1.4.x update, i believe we could set the API Key in the header using "X-Appwrite-Key" to execute functions in the backend using a POST request. How can we do it in the new functions using custom domain as well.

TL;DR

The user wants to know how to set the API Key in the header for executing functions in the backend using a POST request in the new functions with a custom domain. There is no solution provided in the messages.