Welcome to the Community, freightone-offic. I've got you covered on how to get past the null error message when paying invoices in QuickBooks Online (QBO).
You'll encounter a null error message when there's a runtime error that is associated with browser resources or syncing issues. To resolve this, we can access your QBO account using an incognito/private browser. It could be your browser's cache and cookies are corrupted causing unexpected behaviors while saving a transaction. Refer to these shortcut keys:
Mozilla Firefox / Internet Explorer: Press CTRL + Shift + P
Safari: Press Command + Shift + N
Google Chrome: Press CTRL + Shift + N
Then, we can run the Deposit Detail report to check if there are no more null error messages.