In the character customization store in SnapMap, instead of the orange box with the snappoints price, some items just have a red lock next to them and can't just be purchased. How do I unlock these?

After the 6.66 update, the very next snap challenge I completed gave me an armor piece instead of points, but I didn't remember if it was a red locked one, and all challenges since have just given snap points.

I think it would have been a good idea to have some challenges unlock armor parts, while also letting you buy specific ones you want with points, but I've done dozens of challenges since then and I've only ever gotten points since.