There are a few platforms for this sort of thing.<p>Chargify,
Recurly,
Chargebee.<p>I was in the same position as you 4 months ago and was looking for a solution. I looked at a lot of solutions but typically there were two problems. 1) did not have the integration I needed or was not flexible enough that I could build it and 2) they are all quite expensive. The billing is % based billing so if you have even a couple hundred clients the cost is very expensive.<p>I ended up building a billing system in house which will pay for itself in about 6 months compared to the systems above. The system I built integrates with ezidebit for payments and also supports payments by invoice, and also integrates into our accounting system Xero. I can easily add new payment methods if we need to change in the future. It has items to be able to manage plans and also usage based billing.<p>If you have any questions, I'm happy to help, feel free to email me lukevdp@gmail.com