Can you tell me the exact error message when trying to connect your Monzo business account? This way, I can provide the correct solution to it.
In the meantime, let's try connecting the account on a private window. It is to isolate what causes the error message. You can use these keyboard keys to open one:
Google Chrome: Ctrl + Shift + N
Mozilla Firefox: Ctrl + Shift + P
Microsoft Edge: Ctrl + Shift + P
Safari: Command + Shift + N
If it works, we can go back to a regular browser and clear its cache. A piled cache can also be the reason for some unexpected issues on the opened pages.
We can also switch to a different browser like Google Chrome, Mozilla Firefox, Safari, or Microsoft Edge.