Charger/USB port has moisture!

A few days ago, I had same problem with Samsung S8. When the phone was turned off, and I connected to the charger, a message appeared on the screen about moisture in the charging port.

I checked the charging port and I found some black dirt inside. I used tooth brush to clean but it did not reach the bottom of the charging port. Then I used a PCB cleaner ESD brush. It is stronger then a normal tooth brush, and it reached the bottom. After 5 minutes cleaning the problem solved. Sometimes I had to use a thin pointed tweezer to reach all the dirt on the bottom. The dirt was some black sticky material. That caused the moisture message.