I would start by cleaning the contacts with whatever alcohol you can find.
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=== Update (10/04/2020) ===
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Try:
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- Update camera firmware
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- Reset all settings (maybe some setting is making your flash not work)
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If that doesn't help you will have to open your camera to take a look at the connections/wires, for what I see in the picture it has a lot of moisture/dirt that may have creeped inside.