Thank you for posting in the Community. I'm here to lend a hand with importing your payments from outside merchant processing company.
Let's check with your 3rd party processor first to see if they have an app that can connect with QuickBooks. If it isn't available, we can proceed to the next step.
You can import these payments using the Excel CSV file. To successfully import these transactions, your CSV file must be formatted correctly. Please refer to this article for the correct template format: How to import using Excel CSV files.
You can also manually add these payments by entering the transactions directly into your bank register or by creating a transaction form. You may refer to this helpful article for more details: Add transactions to bank register.