Sending messages using MATTR VII can be achieved using a JSON Web Message (JWM) format, you can read more about this approach.
Messages sent to holders based on the subject DID can be read by the MATTR Wallet app to perform actions, there are 3 types of messages supported by the wallet.
Offer a credential using OIDC
Notify a change of revocation status
Start verify using a callback url
There are API operations to construct these messages, they need to be encrypted for the subject DID before sending to the service endpoint of the DID.
As the DID document for
did:keymethod does not contain a service endpoint, messages sent to subjects will assume the MATTR service endpoint as a default
End users of the MATTR Wallet mobile app are able to opt-in to notifications, this will create an inbox on a dedicated wallet backend. As DID's are created in the wallet they are registered against the inbox so messages can be routed to the mobile app using a push notification service. Push notifications are delivered to the wallet as encrypted payloads therefore cannot be read until the wallet is unlocked.
Platform to platform message communications will be available soon using MATTR VII and other interoperable services.
Follow the guide to understand the common steps required to be able to send messages to recipients.