Hey Dypsyman,
I would double-check you have the Steam overlay enabled both globally and for Apex Legends specifically. If that's still not even authorizing the order, I would contact Steam support so they can take a look at anything else that may be affecting the purchase attempt. We wouldn't be able to verify what may be causing that in Steam.
If you do get the purchase authorized in Steam but the coins themselves aren't appearing, that would be something our support can then check into to make sure you get those. Please take a look through this page if that's the case so our support can help out, thanks!