So... I uninstalled the WEBPAY module.
Installed the ZC Square for ZC1.5.7 (Pre webpay)
Configured all the access tokens and secret code... and
... This module is working.

I can proceed with this in the meantime.

Question: Should I remove all the files and run an uninstall SQL for this 1.5.7 module, before going the webpay route?