There is no test actual option for payments. AdRotate Pro doesn’t use API or anything, so any payment you make is real.
The advert, when it runs out of credit/budget, expires. Then in the advertiser dashboard the advert will show as unpaid.
The administrator (you) can start up a transaction in AdRotate Pro > Transactions, click add new and bill the advertiser that way.
For advertisers a “Pay via Paypal” link appears in their dashboard which takes them to Paypals payment page.
Of-course make sure your currency and paypal email are set up correctly in Settings > Advertisers.