I have had a Washer/dryer for 20yrs no smell problems, I use the washing powder tablets you put in a plastic container.
Don,t forget to dry the pool of water that collects in the rubber door seal.
And for those who don,t know yet the grey draining tube must be fixed behind the washer higher than the connection to the drain connection ,otherwise the smell could be dirty washing-up water flowing back from the sink into the washing machine and settling below the drum.