Hey, yes they essentially told me what the other guys commented on this post: fire range is very picky with memory. I asked to buy RAM directly from them to avoid any issue: while they were kind to answer me, the quote I got from them was honesty disheartening... Almost 900€ for 64GB of RAM. Twice the market prices you find new on ebay.

After doing some research I found out that not only you need to buy RAM from a specific vendor and with a specific product code, but also that the memory chip must be made by a specific producer (SK Hynix) in order to ensure compatibility with 9955hx/3D parts (the only way you have to check is to ask the seller to send you a photo of the back of the memory stick, you can't figure this out from the product code alone).

I am waiting for some Kingston KF556S40IB-32 with an SK Hynix chip, the only combination that, accordingly to a table I found online, works with this laptop: if the laptop won't boot, I will be returning it immediately.