Flashing Modded Bios for Asus z87-C

Im at my wits end, Ive tried everything. I am making a pc for my Grandparents, i got them a pcie to nvme adapter, was able to install windows on it but the bios wouldn’t reconise it. So i got the offial bios, followed the tutorials on modding it for pcie boot, but cant flash my bios with it. The EZ flash has the security issue( to be expected), and the afudos says that the modded bios is not the same size as the existing.

Please someone help, I am out of ideas.

Mods cant be flashed with EZ Flash due to security in Asus, regarding tampered files.
Your motherboard doesnt have USB BFB so try the other methods mentioned (Asus section 2-3), be advised that if anything fails the bios must be recovered with an SPI programmer, this is all user side own choice to proceed, good luck.