We do offer limited support for Authorize.net. Basically, while you can use Gravity Press to register WordPress users for 1-time payments without an issue, recurring/subscription payments created using Gravity Forms + Authorize.net have some limitations in that they will look and act like 1-time payments in MemberPress instead of recurring transactions.
The practical effect of this is that if a member wants to cancel/upgrade/downgrade their membership from within MemberPress using the Member Account/Portal page, they will not be able to. Instead, the site admin will need to handle all cancellations/upgrades/downgrades manually. This is due to the limitations related to Authorize.net and is outside of our control. If you need to be able to offer such account-management features to your members, we recommend using Stripe and the Gravity Forms Stripe add-on.
*This is noted on our product information page.