I bought License Tier 2

The DKIM do not want to be verified, my cPanel say it is too long (when I add a domain)

How do I add a mailbox (an user)

And I am confused... In usage, what are those :

"Email Credits - Your current email credits state."

"Current Month - Your current monthly usage."

Both are shows as 0

What is the credits, and the 50k, is it 50k email I can send per month?

Thanks