What happened when you tried to use them with Starbucks? I had no problems using them to purchase credit in the app. If I recall correctly, they were basically just Mastercard debit cards that were loaded with $12 each in my case, and presumably restricted to certain merchant codes. Only down side was that Starbucks doesn’t allow random amounts, so I wasted $2 on each cert since I could only load $10.

My most recent experience with this was in October 2024.