I still can't figure out why you cannot link to OnlineGAR.
Their system still works perfectly for UK passport crew/passengers.
Example
i was at L2K on Monday with 3 POB, all UK passports, and filed my GARs via OnlineGAR.
OnlineGAR sent the required email to L2K customs which saved me doing it and on return to the UK the UK Border Force welcomed me like all others who do not have any paperwork with no complaints.