It seems that the requirement to support 287 wasn't added yet for the /sen and /sren resources.
The RFC 9148 requirement:
Content-Format 281 MUST be supported by EST-coaps servers. Servers MAY also support Content-Format 287. It is up to the client to support only Content-Format 281, 287 or both.
needs to be updated to make 287 a MUST on the server side, with the exception case defined in 6.6 for /crts.
( Triggered by the new issue: https://github.com/ace-wg/est-oscore/issues/38 )
It seems that the requirement to support 287 wasn't added yet for the /sen and /sren resources.
The RFC 9148 requirement:
needs to be updated to make 287 a MUST on the server side, with the exception case defined in 6.6 for /crts.