I’m having the same issue of this post.
is there any update on the matter?
register_rest_route was called incorrectly. The REST API route definition for zapier/v1/token is missing the required permission_callback argument. For REST API routes that are intended to be public, use __return_true as the permission callback. Please see Debugging in WordPress for more information. (This message was added in version 5.5.0.)
Best answer by SamBView original