regarding domain mapping and pro site plugin

@Jack Kitterhing.

Hello jack i have installed and configure the domain mapping plugin but did not understand how it works, as i know it must works like when user upgrades his site then before payment system will ask user to book a domain , user type his domain name and book it from my side by help of domain mapping plugin then he will be redirect to payment gateway , in this way he will finish upgrading.

One more thing after upgrading my site i can still see upgrade button on top right why ?
please assist me as i have to update to my client we have very less time to solve it.

Many thanks