Can't setup facebook shop and no porper product syncing

[WiinShoop]

I've been trying for days to get some Facebook issues solved, specifically the "invalid or missing images" one.

Since the product came directly from shopify, the pictures are also imported from there, I've manually checked each and every one of them to be in the correct resolution, format and size; and it still shows the error.

Worth mentioning : even when I add a JPEG image to shopify and decide to re-download it to check, it's in jpg???

Thanks for your help