My iphone keep saying “Charging unavailable”

About 2 months ago I accidentally went in the beach water with my phone in my pocket, mid leg to waist deep. When I realized it was too late. My phone kept saying “Charging Unavailable: Liquid detected” after that, so I let it dry and fortunately it worked.

However, now and then I get the message saying “Charging Unavailable: Liquid detected” just randomly, while my phone is dry. I’ve used compressed air to try to clean off any sand or anything in the lighting port, but I don’t see much coming out.

What do you recommend?