Irregularly recurring payments with PayPal

Question

Starbucks has the option to auto-refill your store card via PayPal.

I authorize them only once and they charge my card each time my card balance drops below $15 or whatever amount I specify.

I thought this was just normal 'subscription' functionality I could leverage for my own site, but it seems to me that the normal functionality of 'subscriptions' or 'recurring payments' only supports regularly recurring payments in intervals of weeks, months, or years.

Basically, I need to be able to obtain authorization for future payments that'll allow me to charge the PayPal account whenever a billing trigger (eg the user attended an event) occurs, without the user having to approve it each time.

How can I do this?

Answer 1

I've since discorvered that PayPal Vault would be the way to do this in PayPal: https://developer.paypal.com/docs/integration/direct/rest-vault-overview/

Other (perhaps better) options are Stripe or WePay and probably other payment providers that let you store credit cards on their servers and charge them later on.