A payments product cannot ship because it works. It ships when a certification body agrees it works — and the standards involved (ISO 8583 on the wire, EMV in the chip, PCI DSS around the whole thing) are unforgiving about details.
Helped start Mosambee in Mumbai, one of India's early mobile point-of-sale companies: the app, Java backends, REST APIs, ISO 8583 message formats, PCI DSS compliance, EMV chip-and-PIN, and hardware integration taken through certification.
This is where the pattern that runs through everything since was set: the technical work is only half the job, and the other half is clearing whatever external body stands between the product and the market.