Originally Posted by Xandrios

Try to avoid touching the booking, in any way, using an app that is logged in to another FFP. That will almost always cause the miles to credit to that FFP.

Last time I flew SAS I had booked the (Go Light) ticket on flysas.com, provided my flying blue FF number, and checked in using a web browser. Boarding pass showed "KL/Elite Plus", Group 1, SkyPriority and the miles were credited to Flying Blue normally. Also received checked luggage for free based on status. Don't remember how exactly, but I do still have some of the older SK Boarding passes loaded in my Pass app on the phone, so a digital boarding pass can be retrieved that way. Possibly from an email.

In your case I would suggest logging out from the SAS app before continuing with Flying Blue. Opening such booking with the SAS app while logged in will make those miles go to EuroBonus instead of Flying Blue. And make sure that, on the flysas website, the Flying Blue FF number has been added to the booking beforehand.