What are reliable high risk payment processors for start-ups?

Shopify cancelled our ability to process payments through their gateway. I need a third party payment processor that can seamlessly process credit card transactions at reasonable fees that integrates with Shopify and also does not require historical P&L or personal guarantees.

This is a start-up that is selling hardware online, and we just need a way to sell our product and process payments. We don’t have sales yet. Bankful.net did not work as they require a personal guarantee which we are not comfortable doing.

Thank you