I am sorry I just realised that I was not specific enough. I've been wanting to build a service platform to offer services where people were not restricted to use a certain currency for certain services like paying a transaction fee. So imagine something like MEW for ethereum with the difference that you can pay tx fees with Euros or BTC.
My problem is this right here: Braintree acceptable use policy: https://www.braintreepayments.com/legal/acceptable-use-policy
Wouldn't Paypal block my API key as soon as the visit my site? Here their acceptable use policy: https://www.paypal.com/us/webapps/mpp/ua/acceptableuse-full