Looking for advice: how to collect licence fees for software?

See more:

licensing

payment-gateway

So the best solution I have found is paypal, but it's not perfect.

We have two products (in this package). Each have bulk discounts.

The only way I can seem to get that to work through paypal is to have a plan for each licence holder. The plan will have ProductA & ProductB x Qty items as well as a ProductA & ProductB discount items where applicable. If the licence holder reduces the qty of either then I'll update the plan to reflect this. If they increase the licence qty then I will have to ask for authorization details again and create a new plan (to get around the 20% increase limit).

So, it's all just trying to twist Paypal to do what I need but: How is it normally done? I asked if we could just invoice our licencees but I laughed at (still dunno why; who are we marketing to?)

If not via invoice / payment, how is software usually payed for?

Thanks
Andy ^_^

What I have tried:

Paypal is the best option. Looked at SagePay (has some very odd restrictions) and GoCardless (BACS payments could take 6 days to return. That's too slow (so I've been told)