post https://api.partnerstack.com/api/v2/transactions
Creates a new transaction
Note that customer_external_key or customer_email can be provided in
place of customer_key to reference the customer. The customer_key
referred in this endpoint corresponds to the internal customer key generated
by PartnerStack.
These customer reference fields are required, but mutually exclusive
(i.e. you must provide exactly and only one of the three).