ipn from paypal not creating transactions

IPN history shows correct Notification URL, HTTP response code 200 and Delivery status Sent. However no trasactions are created.

I've added '$appointments->log' in handle_paypal_return function after global $appointments (line 707). Nothing showing in log file.
Created a test file in domain root level to test that ipn can get through the site and it did.

It looks like wp-admin/admin-ajax.php?action=app_paypal_ipn not reaching 'function handle_paypal_return'

I'm testing in Sandbox.

Can you help?

Thanks