Check Verification is Called IBV - (Internet Balance Verification) which is actually a 3rd party software integration.

Your merchant is prompted to log into their Bank Account, which verifies routing, account #, there is a positive balance (it does NOT disclose Bank Balance)
at that moment for the check to clear. ***The check still could be a NSF !!!

Keep in mind all of these systems, Genie Check and my friendly competitors, these checks are NOT Guaranteed.
**Check Guarantee is a service that is available for an additional fee from certain providers.

As an example, ACWorks, it takes about 5 days for funds to actually deposited into your bank account.,
The utilize a "Settlement Account" which provides protection against NSF/Return to Make, etc. checks hitting your business bank account.

ACHworks provides a report of how many checks cleared and what was returned & why

https://www.vericheck.com/ach-return-codes/