Hello, sbae. 

The payment field should be zero after creating a bill payment to link the vendor credit and the bank deposit. 

But if not, then I suggest reaching out to our Customer Support to further check your account. Their tools can securely get into your account to further check what’s causing the error and help you resolve it. 

You can do it by going to the Help icon at the top right of your QuickBooks Online (QBO) account. Follow the steps below: 

1. Go to the Help icon to connect to a live support agent. 
2. Click on the Contact Us button and provide some details about this concern.
3. After adding some insight, click on the Let's talk button. 
4. Lastly, select the Get a callback button to arrange a call from them.

See this article for detailed guidance: Contact the QuickBooks Online Customer Support team.

You might also want to browse these links to know more about vendor credits: 

• Enter a credit from a vendor
• Applying vendor credits

Let me know if there's anything that I can help. Have a great rest of the day!