If you have a US bank account, it's hard to beat Stripe (https://stripe.com/ https://stripe.com/). They allow you to process payments without forcing users to s

If you have a US bank account, it's hard to beat Stripe (https://stripe.com/ https://stripe.com/). They allow you to process payments without forcing users to sign up for a third-party service, and they handle compliance and the heavy lifting of recurring billing. Perhaps most importantly for your use case, they allow you to combine small charges on a monthly invoice, which reduces your processing fees (because fees on small transactions are otherwise insane). They also support euro-denominate transactions. Integration is well-documented and easy if you're comfortable with RESTful APIs. If you prefer to bill users for each transaction instead of invoicing, Amazon Payments might be a better solution. I've never used them, but they offer a fee structure that makes small transactions less painful (https://payments.amazon.com/sdui/sdui/business?sn=devpricing/fpspricing https://payments.amazon.com/sdui/sdui/business?sn=devpricing...). Good luck!