You'll want to double check that your payment provider is correctly set up on Shopify, which should be one of these three:
1) Shopify Payments
2) Paypal Express
3) Authorize.net
4) Stripe
Please note our app does not handle the checkout process, that message you are seeing is coming from Shopify.
I recommend getting in touch with Shopify regarding this, so they can assist you.
One quick way to see the status is to go to Shopify admin dashboard --> Settings --> Payments and see if there are any warnings/ error messages displaying for action items you need to do.
Also sometimes, it just take a week or so after setting up a payment gateway to get officially approved.
Our app handles recurring billing, and Shopify handles processing payments.
Processing payments is handled by your payment gateway. If you are seeing this message, there is an issue with your payment gateway, not our app.