Good morning, @mayc,
Thanks for the question. If you're sending an invoice to a customer and they are paying online, they are entering the information themselves, so that is the authorization. We don't have an authorization form specific to those types of transactions. If you would like a form for those transactions, there are multiple templates online that you can use.
If you are setting up a recurring payment where a customer is charged on a monthly basis automatically, there is an authorization form you can access from the Merchant Service Center. Here are instructions on how to get that form:
Get authorization for a recurring charge
Thanks,
Lucas