We're using the API to create a client and also want to set both the PAYG and Monthly billing settings.
However we are running into the issue that when we send both details via the API - only the monthly option appears in a clients account (which is what we set last).
My goal is for the customer to be able to choose their preferred option when they go to send the first campaign.
Is this a limitation of the API? or is there a way around it?
Unfortunately it's not possible for clients to choose their preferred option at this stage. I've recorded your request for this functionality though. In the mean time you'll have to get this information from the client and switch them yourself.