I think this might be because Plasma/Barn has merged the client and server, while Feather provides mappings for the client and server separately. This means for Plasma/Barn the version is just called 'b1.7.3' while for Feather there are two versions, 'b1.7.3-client' and 'b1.7.3-server' and thus it can't find a match and says there's no way to translate between the two.
But it should be possible to translate between them, as they target the same MC version.
I think this might be because Plasma/Barn has merged the client and server, while Feather provides mappings for the client and server separately. This means for Plasma/Barn the version is just called 'b1.7.3' while for Feather there are two versions, 'b1.7.3-client' and 'b1.7.3-server' and thus it can't find a match and says there's no way to translate between the two.
But it should be possible to translate between them, as they target the same MC version.