Hi and welcome to the forum
Have you tried alternative chargers as well as cables?
If your phone is still under warranty that doesn’t cover you taking the bottom module out unless instructed to. Usually Fairphoen will ask you to do non invasive tests and if that doesn’t work and you have a valid warranty they will ask for you to send it.
It isn’t expected that you should try and resolve such issues mechanically.
If on the other hand you do not have a warranty
- then removing and cleaning the contacts is always a good step,
- as well as cleaning the USB port
- You can also breakdown the bottom module to better clean it.
FP3 Bottom & Top module breakdown
The problem with remote support is the waiting time, hence the tendency to do a DIY
Another option is to see if there is a #fairphoneangel near you that may be able to help