A buy-to-let mortgage is not suitable for funding serviced accommodation. You will need a commercial mortgage if you intend to fund serviced accommodation.
In a buy-to-let mortgage, the property is going to be rented out for at least six months on an annual rental agreement, and ideally for a longer period of time.
In the case of a mortgage that is specifically for serviced accommodation, the maximum amount of time that your property can be let to the same occupier may be limited, so when you are trying to market your property, you should make sure you are aware of any restrictions.