You need to turn on the Yahoo! Mail security app feature, acctili.

My colleague Catherine_B  provided a detailed article that you can refer to.

QuickBooks will not accept my web mail password.

The steps are only applicable if you're using Yahoo! Mail or Gmail as your email provider.

You can also check this article if you haven't Set up email service  yet.

Let me know if you need anything else. I'm here to help.