Picked up and began running Pokémon shield the other day. Following the guide but every time I hit the wild area, take the two death warps and go to buy the quick balls they aren’t available. It keeps offering me heal balls. Any idea what the issue could be? Thanks.

Make sure you set your clock to 11:45pm before booting the game. The idea is that it takes ~25-30min to reach the wild area, so you want to start the game on Day 1 and have it roll over to Day 2 before you do the wild area. If it's still Day 1 (sounds like it is based on you getting Heal Balls), then you will not get Quick Balls there

Also it's important that you set the clock BEFORE starting the game. If you set your clock after, then time based events (like the Watt traders changing) won't happen