We built this for our own store first.

TandemPay started as an internal fix. We were running a WooCommerce store in a category processors do not like, we had been through a freeze and a held balance, and we had already tried the usual answers: a second store with a redirect, then manual invoices, then a third-party checkout that took a cut and looked like exactly what it was.

None of them held. The redirect cost us orders at the moment of payment. The invoices were unworkable at volume. What we wanted was a checkout that behaved like a normal checkout, on our own domain, while the store our processor reviewed was a store we had actually built for that purpose.

So we built the pair of plugins that does that, ran our own business on them, and kept fixing the parts that broke. The product you are looking at is the version that came out of that: not a prototype, and not a clever trick, but the thing we rely on.

Same architecture we run ourselves. Packaged properly, documented, and supported.