Mews sends a notification email when a channel manager reservation was forwarded with a space or rate code that is not mapped in Mews. The unknown code needs to be added to the channel manager integration to be able to assign the correct rate or space to the booking. If this code doesn't exist, then Mews will assign the default information to the reservation.
Go to Menu > Marketplace > My Subscriptions > Channel manager settings > Channel manager rates & channel manager categories to see the existing mapping for rates and space categories.
The channel manager ID's for each rate and space category are the codes which are used to communicate with the channel manager.
Note: codes are case sensitive and that capital as well as lower case letters need to be copied exactly.