automatic renewals with Authorize.net

I appreciate your detailed explanation.
We do in fact use recurring bill (primarily) - literally hundreds of active subscriptions.
It's not that it's impossible to change processors, but this will be somewhat burdensome for us as well as our clients to get everyone switched over.
I can understand your position and again, thank you for the detailed explanation.

I took your advice and added 'Paypal Pro' feature to our existing Paypal business account so we can process credit cards without subscribers needing to have or setup a PP account. I configured the API username, pword, and signature fields in CBSubs with what Paypal issued to me. I then took the notification URL CBSubs generated and put that back into Paypal in their IPN (Instant Payment Notification) field.

I confirmed that API type on our account is 'Website Payments Pro' and not the 'Payflow' option.

I created a dummy subscription that auto recurs daily to test CBSubs being updated when recurring charges are made. It does not. This is what Authorize.net stopped doing correctly. Any ideas on what could be causing Paypal not to work properly? All fields seem to be configured so I'm at a loss.

joomla 3.9.10 with latest build of CBSubs

There's no notifications from PayPal Pro at all within CBSubs > Notifications? Any errors logged within CBSubs > History Log? There's no issues reported for PayPal Pro at this time and appears to still be working in my tests. Ensure your install is completely up to date with latest build releases. Below is the only known issue, but has been fixed.

forge.joomlapolis.com/issues/7687

If no notifications from any gateway are not reaching your site the problem maybe your site blocking them. Could even be a server firewall blocking them.

I just verified there are no Notifications at all for the recurring charge, only the initial payment.
There is however an error posted in the History Logs: paypalpro Paypal IPN fraud attempt. ERROR: paypal subscription IPN type subscr_payment for a basket without auto-recurring items: Invalid transaction. Please contact site administrator to check error log.

the odd thing about that error message is that it states the basket had no auto-recurring items. But it does. The basket has a single test subscription set to charge $1 good for 24 hours a total of 3 times (which would be initial charge + 2 daily recurrings). Paypal is processing the recurring charges daily as it should. It just is unable to report back to CBSubs that the payment was processed.

Is restricting the auto recurrings to 3 instead of setting it to unlimited possibly the issue causing it to think it's not Auto-recurring?

Review the subscription within CBSubs > Subscriptions and see what "Autorecurring Type has been set to. If set to "Autorecurring without notifications" it's using CBSubs scheduler to validate recurring payments, which you can find the URL to trigger within CBSubs > Settings > Global. If it's set to "Autorecurring with notifications" it'll renew automatically from recurring IPNs. If it's set to "Not autorecurring" the basket for some reason was stored as a single payment. It should be set to "Autorecurring with notifications". I've reviewed the gateways code and I don't see a scenario where a recurring payment couldn't be set to that unless the initial payment API call failed.