iPhone charging issues (iPhone 6s)

I just bought a used iPhone 6s, I turned it on and it has the red battery icon on it. I thought to charge it so I got my official iPhone lighting cable and official charger brick.

So I plugged it in and I got the red icon with the white cable with a charge symbol next to it, after about 15 min I checked it and its still in that same thing, red icon.

Does anyone know what I should do? I cleaned the charging port out, with a wooden toothpick it was dirty, same issue. I thought the lighting port is fine because the phone displayed it charging when I looked at it again so I don't think that needs to be replaced is it the battery or the charging port or maybe something else.

Does anyone know the iPhones issues?