Supporting cross-border payments of an asset through the Stellar network requires cooperation between a sending anchor (SA) and receiving anchor (RA). In this section, we'll only go over the steps necessary for building a SEP-31 receiving anchor, but documentation for building a sending anchor is in development.
Specifically, we will go over the SDF's Tools and References as well as all three stages of the development process:
The Basic User Experience
Unlike with SEP-24, SEP-31 involves a sending user (SU) and receiving user (RU), so both users' experience is described here.
Note: SA's are not necessarily wallet applications. This means the SU may not interact with a mobile application, but could go to a website or physical remittance location instead. Obviously, this affects the SU experience.
Generally, the experience of the SU and RU would look something like this:
- The SU opens an app, website, or goes to a physical remittance location
- The SU specifies the asset and amount to send, and the asset that should be received
- The SA finds the appropriate RA for the asset, authenticates with the RA, and parses the RA's requirements for sending payments
- The SA collects both the SU and RU KYC information requested by the RA from the SU, as well as the transaction information
- RU's should not have to take any action to receive a cross-border payment
- However, it is possible to require action from the RU if absolutely necessary
- The SA registers the RU and potentially SU with the RA via SEP-12
- Once the RA is ready to receive the payment, the SA makes the Stellar path payment to the RA using the SU and RU assets
- Once the RA receives the path payment, it attempts make the associated off-chain transfer (usually bank transfer) using the KYC and transaction information sent by the SA
- If the transfer to the RU fails, the SU will be notified by the SA to update the invalid or missing fields, and the RA will retry once the SA sends the updated info.
The RU should then receive the funds sent by the SA once the RA has the necessary to make the final transfer.
Note: The final off-chain transfer by the RA may not be a bank transfer. For example, the destination could be a mobile money account managed by the RA. The methods used to transfer the payment off-chain to the RU is up to the RA, and SAs should be aware of the off-chain transfer methods of their partner RAs.
Interoperability and Stellar Ecosystem Proposals
As mentioned, this section will outline how to implement a SEP-31 receiver, but these servers require SEP-1, 10, and 12 to be implemented as well. SEP-1 is described in this guide, and SEP-10 & 12 are described here.