Add a specific error when inviting a remote cluster to a remote channel (#28255)

server/platform/services/sharedchannel/service_api.go

@@ -150,7 +150,7 @@ func (scs *Service) InviteRemoteToChannel(channelID, remoteID, userID string, sh
 	// (also blocks cyclic invitations)
 	if err = scs.CheckCanInviteToSharedChannel(channelID); err != nil {
 		if errors.Is(err, model.ErrChannelHomedOnRemote) {
-			return model.NewAppError("InviteRemoteToChannel", "api.command_share.channel_invite_not_home.error", nil, "", http.StatusInternalServerError)
+			return model.NewAppError("InviteRemoteToChannel", "api.command_share.channel_invite_not_home.error", nil, "", http.StatusBadRequest)
 		}
 		scs.server.Log().Debug("InviteRemoteToChannel failed to check if can-invite",
 			mlog.String("name", rc.Name),