Is there a service for integration with the online checkout?

Question

API

Hello!
It has its own accounting system, which must be connected to some online cash register and with the support of the Honest Sign system. Its system runs on PHP. We can transfer marking codes from our inventory system.

Are there any ready-made services? For example, there is an MTS Cashier, but it does not have the ability to transfer marking codes from an external system to an order.