I have been reading the Sage Pay API documentation and had a question about the use of merchantSessionKey when sending a Payment transaction.
Do I always need to send the merchantSessionKey used when I created the cardIdentifier when making a Payment? Or can it be any valid merchantSessionKey?
I am trying to work out whether I need to save the merchantSessionKey locally alongside the cardIdentifier when I call POST /card-identifiers so I can use in future transactions associated with this cardIdentifier.
Many thanks
You need to supply the same merchant session key when you do the initial transaction. If you have saved the CardIdentifier to use at a later date, you don't need to supply a merchant session key when you do subsequent transactions...
(remember to flag the transaction as "reusable":true, though)