Error 403 when connecting

Installed and activated the plugin.
However, even with Jetpack installed as well, I get the following error when trying to connect WordPress in Zapier:

403 Forbidden: Access Denied. Please see common causes and fixes for 403 errors at https://zapier.com/help/doc/common-problems-wordpress#403-forbidden-error.

The common problems page does not help at all unfortunately.
Tried everything listed there, no luck so far.

Does anybody know a solution for this issue or a different working alternative?

Many thanks,
Michael