What’s the substrate? Are you going on floorboards or have you ripped it back to joists and fitted ply?
Either way you want to make sure your joists are solid, and fit noggins if necessary. I would usually then overboard in at least 18mm ply, fixed at 150mm centres. Then glue and screw 6mm cement boards after having primed the ply first. The cement board joints then need to be taped which an alkali resistant tape bed in some tile adhesive. Pointless using ditra in that situation as it does nothing to strengthen the floor