How do I get access to the NatCash merchant API?

Unlike MonCash, NatCash doesn't publish an open developer portal with self-service sandbox keys. Integration access goes through Natcom's business / merchant team:

1. Register as a NatCash merchant (business account). Have your business documents ready: patent (patente), NIF and ID of the legal representative.
2. Ask specifically for API or e-commerce integration. Say what you need: accepting payments on a website or app, confirmation callbacks, and whether you also need payouts.
3. You'll receive the technical documentation and credentials under agreement. Base URLs, authentication and a test environment come from Natcom directly, and they can change. Always build from the documents they give you, not from code found online.

While you wait (it can take a while), design your code so NatCash is a pluggable provider next to MonCash (see the payment-provider interface question), and offer a temporary manual flow for NatCash customers so you don't lose them.

Tip: ask Natcom early for the callback or notification mechanism, and how to query a transaction's status by your own reference. Those two features determine how reliable your integration can be.