As I understand it, Charlton faxed the papers to the FA at 16.59 (the window closed at 17.00) whereas the FA said they'd been sent after the window closed. Charlton disputed it, and it seems they've won.
https://www.londonnewsonline.co.uk/...getting-answers-on-deal-for-brighton-striker/
Don't think Charlton did get the FA to agree. Brighton cancelled his contract making him a free agent to sign for anyone. Good moral move by the club for all concerned.