I know some things suggested here, will be a bit obvious at first, but let’s take it from the top.
# Make sure nothing is inside the charging port and/or the charging cable. If you see dust or lint/dirt inside the port or cable, gently take it out with a toothpick or slim tweezers. Make sure to not force or put pressure as you are doing that, as it could bend/break the charging port.
# Try different cables/power box and different power outlets.
# Take a look at the USB-C on the phone, and make sure the port is not bent or broken.
# Turn off the phone. Then take the phone with the cable cord connected (with no power box), and plug into a USB port on a computer/laptop Turn the computer/laptop on. Leave it plugged in for about an hour to two. Then, take the phone and disconnect it from the USB, and plug it into the power box and onto a wall power outlet like normal. Leave it until it is fully charged. Then you may turn it on.
# Make sure the water damage indicator has not changed color or dissolved. (Take SIM tray out, and a white square sticker should be seen inside close to the edge of the SIM tray.) You may need a flashlight to be able to see it better.
# Depending on how long ago you got the device, if it’s under a year, it has the one year warranty from your wireless carrier. If not, but you have insurance on it, you can put a claim, but you may have a deductible. If the device does have water damage and/or is damaged by anything else other than technical problems, your carrier may have you pay the deductible or pay the remaining balance of the phone if you are on a payment plan, in order to get a new device.
Hope those steps help.