Problems checking out with Payflow Pro after Delta Migration
Our Magento 2.2 install was working fine with Payflow Pro after doing the data migration from our 1.9 install, but ever since completing the Delta migration, we're able to check out with Payflow Pro (the transaction is seen on Paypal), but it doesn't return back to the shop afterward. There appears to be an error appearing during checkout, but the message itself is completely blank - we're receiving a few different errors in exception.log, but even they don't always get logged:
PayPal gateway errors: Field format error: 10412-Payment has already been made for this InvoiceID
PayPal gateway errors: Generic processor error: 11607-A successful transaction has already been completed for this token
I've looked into both of these errors, and the solution seems to be a mix of things, none of which are working for us:
1. I've updated the settings in the Paypal account to allow duplicate invoice IDs
2. I've increased both entity IDs in the database (and, after no change, reverted them back to what they were previously)
3. Enabled IPN in the Paypal account (we never needed this before, but Paypal Tech Support recommended trying it - no change)
Again - the issue only started happening after Delta migration completed, and the transactions are still going through to Payflow, they're just not coming back to our shop afterward (and, as such, no order record is created in Magento).
Please advise - Magento has been fighting us at every stage of the install/upgrade/migration process and it's very frustrating to see it stop working this far into the project.
EDIT: Payflow is also in "Debug Mode", but nothing is being logged in "debug.log", and there is no other "Paypal.log" file in /var/log.
EDIT 2: We're noticing that some orders are coming through with 10-digit IDs, when they were 9-digit on Magento 1.9 - could that be a part of this issue? If so, why did that change?