Here's a recent suggestion that was published into a KB article!
Sophos XG Firewall: How to configure a RED 50 with VLANs
[locked by: SupportFlo at 12:56 PM (GMT -7) on 2 Oct 2018]
[unlocked by: SupportFlo at 2:04 PM (GMT -7) on 16 Oct 2018]
[locked by: SupportFlo at 2:04 PM (GMT -7) on 16 Oct 2018]