I cannot log into my Yahoo account, it says my password is incorrect

BusyCal or BusyContacts is unable to sync with your Yahoo account because it now requires that third-party apps use an app-specific password to sync with your Yahoo account. Your standard Yahoo password will not work.

Follow the instructions on this page to generate an App Password to use:

https://help.yahoo.com/kb/SLN15241.html

Note: You might have to disconnect and reconnect BusyCal / BusyContacts to your Yahoo account after creating an App Password, as follows:

• Select BusyCal / BusyContacts > Settings > Accounts, click on the Yahoo account in the left sidebar, then click the minus (-) button to remove it.
• Then re-add the account by clicking the plus (+) button, selecting Yahoo as your server type, and entering your Yahoo ID and the new app-specific password you created above.