QB Bill pay trouble.I entered an email for a vendor that is being used for another account. Vendor cannot sign up with it.I changed the email in QBO vendors but?

Try opening your QBO account on any private/incognito browser.

Hello there, milespotter.

To better assist you, could you please provide more details it? Did the vendor receive an error message when attempting to sign up, or did they encounter any other specific issues? I would appreciate getting more information from you. This way, I can provide the right amount and solution to your question.

In the meantime, you can let them check the spam or junk folder. Sometimes, automated emails can end up in these folders. 

Visit again in the Community forum. I'll be around to help anytime.