When you setup your account, you specified a default Merchant Account. This is what we’ll use for all of your upsells.
Alternatively, you can specify a specific merchant account to use when processing an upsell.
This is great, for example, if you want to process your main product sales on one merchant account, but your upsells on another, or if you have multiple business lines, each with their own merchant account.
When posting to your InstaCharge URL, add mid (for “Merchant ID”) to your GET or POST parameters with the value being the ID of the Merchant Account you want to use.
For example, you might change your URL from https://instacharge.com/v1/?hash=YOURSECRETHASH to https://instacharge.com/v1/?hash=YOURSECRETHASH&mid=5 to use Merchant Account #5 in your Infusionsoft account.