An Issue with Remote event receivers on SharePoint Online: Not firing

I have a project which requires adding remote event receivers to SharePoint Online Lists from an Azure function app. I am able to add the RER but it never fires.
It is being added under the App's context and the App has the required permissions to the tenant of course. The RER shows as added with the right endpoint (this is a function url ). The function url is never being hit when an Item is added to the list or updated. And absolutely no logs which mentions any error.

Has anyone ever had a similar situation and knows anything about the issue? Please help.

Thanks
Ayesha