How are you? Obviously you would have to pay to play and they probably would make you buy a day pass at the resort in El Portillo. I believe there are courts out in La Esperanza Residencias in Barbacoa which are in expensive to use. I have seen them advertised in LT7.
Esperanza Residence has tenniscourts. They are not free. Which is normal i think. Somebody invested money, needs to maintain it and you are using it.
If you want to play tennis for free, playa beach-tennis.