QuickBooks Online won't accept the banking information of your contractor if the direct deposit is not yet activated. You can activate the direct deposit by following the steps below:
Go to Workers from the left menu.
You’ll see a banner that reads “Pay contractors with direct deposit”.
Click the Check it out button.
Click on Turn on Direct Deposit.
After that, you need to activate your direct deposit by clicking the Get started button.
Click Set up direct deposit.
Choose the Add bank hyperlink to enter your banking credentials.
After entering bank information, a test transaction must be entered to verify the bank account on file. No need for bank verification if you bank with one of our eight partners listed in the Enroll in direct deposit article.
Once done, you can invite your contractor to provide their W-9 business and make sure that they input the correct bank information.
However, if you already set up a direct deposit and the issue persists, I'd suggest contacting our Customer Support Team. They can further investigate why QuickBooks don't accept your contractor's banking information. You can reach them through the contact information found in this link: Contact the QuickBooks Online Customer Support team.
I'm adding these articles that will guide you in paying contractor with direct deposit, how to file 1099 for your contractors and it's troubleshooting steps: