Hi,
ok, so Ive replaced the maps file as per your instructions, enabled the Maps Javascript API on google, but all I get is Sorry! something went wrong on the front end
Have you deleted the old one? you cannot have new gmap.php and old gmap.php (renamed) in the same folder because they will have the same PHP classname.
Is this maps api not a chargeable system within google, per use? If so I wont be using the feature at all, you should program it for openmaps instead.
Openstreetmap have some limitation, like geocoding APIs (it uses nominatim that has a strict Usage Policy).
Google Maps is free? Google maps should give to all customer 200$ of free credit for each month, so it is free for 99,9% of customers (not for huge systems, however difficult to manage with Joomla). But to works it require that you enable billing and associate a payment method with your account.