Shopify didn't approve our request for Billing exemption and suggested to write here on the forum.
Our app provides the opportunity to send SMS and we increase customer balance after getting success status on the usage charge method from Shopify Billing.
After it the merchants (mostly spam stores) use the balance to send spam messages, it can be up to 1000$ an hour and then they just uninstall and do not pay the invoices (their store are being frozen by Shopify - but that's not a big deal for them, cos the stores are empty).
While we need to actually pay for those messages to our SMS operator.
Does anyone have the same issue? What can we do in this situation?