This problem started for me a few days ago. It was saying moisture in USB when headphones were plugged in but was fine when charger was plugged in. I spoke to support and they suggested repairing my software. This did absolutely nothing other than make me lose some data because the backup apparently doesn't capture everything. Being ex-IT support myself the information told me it's probably an issue with the adapter itself and not the phone so I bought a new adapter off of amazon for a few £ and it's working absolutely fine. The old adapter (the one I received from Sony) is still saying moisture so I think it's definitely the adapter. I hope this helps.
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