Redirection Help and Login Help

[tanzeelniazi]

Hello all i need your help
I want to know if i have forum name example https://www.mainsite.com/ and i have paypal subscription but i dont want to receive any payment in https://www.mainsite.com/
now i want to receive payment from https://www.Anotherdomain.com/ how ?
I mean i see 1 forum name https://www.mainsite.com/ after when i click or try to buying vip i see another link https://www.Anotherdomain.com/payment.php
so when i open forum 654321.com i see he says first login its mean i need to create new account in https://www.Anotherdomain.com/ but if i use login detail from https://www.mainsite.com/ its working HOW ???
and when i am login in https://www.Anotherdomain.com/ i see only Payment.php page
So my question is How can i do this

--------------- Added [DATE]1434306856[/DATE] at [TIME]1434306856[/TIME] ---------------

How https://www.mainsite.com/ forum login detail working in https://www.Anotherdomain.com/ ???
How payment page only showing in https://www.Anotherdomain.com/ ???