This is how we will get a 'subscr_id' type thing for recurring payments.
POST https://{domainname}/{version}/{merchantId}/payments/{paymentId}/tokenize
Then to use it we create a payment
https://developer.globalcollect.com/documentation/api/server/#__merchantId__payments_post
setting the 'token' field in the cardPaymentMethodSpecificInput
https://developer.globalcollect.com/documentation/api/server/#schema_CardPaymentMethodSpecificInput