FLR after initial approval - include approval letter?

I don't know why but I thought I should include the approval letter together with the passports and other stuff when sending documents to switch to HSMP. However I couldn't find it in the guidence and document checklist. Of course cannot phone HO - the line is always busy..
Could you please share your experience - have you included the approval letter or that's not necessary?
Thank you!

You should include the approval letter, plus send a notarised or JP-witnessed copy with any spouse/dependant application for EC/Leave to Remain. I suggest keeping a notarised copy for yourself, too.

W.