To fix the issue of vendor credits being automatically applied when you pay a bill, you need to disable the Automatically Apply Vendor Credits setting in QuickBooks Online. To do this, follow these steps:

• Go to Settings > Accounting > Preferences.
• Click the Bills & Payments tab.
• In the Credits section, uncheck the Automatically Apply Vendor Credits box.
• Click Save.

Once you have disabled this setting, QuickBooks Online will no longer automatically apply vendor credits when you pay a bill. You will need to manually apply vendor credits to bills as needed.

If you have already disabled all automations in QuickBooks Online and the Automatically Apply Vendor Credits setting is still enabled, then the issue may be caused by a third-party app or integration. To troubleshoot this, you can try disabling all third-party apps and integrations and then see if the issue persists. If the issue is resolved, then you can re-enable the third-party apps and integrations one by one to identify which one is causing the problem.

If you are still having trouble disabling the Automatically Apply Vendor Credits setting, you can contact QuickBooks Support for assistance.