You collected all 20/20 tokens but it's not claimable or you can't change M4's camo blueprint to Black Gold Royal.

Check Inventory for ??/100

To get the Black Gold Royal skin for M4 you need to actually get 20 tokens in 5 seasons.

You can go to Loadout and then Inventory to find the "[Shard] M4 - Black Gold Royal" to see your progress.