Cards failing after CC checker

[laggiler777]

I want to clarify that before this, my credit cards were working fine for App Store purchases.” “After I used a CC checker, transactions started failing. To be clear, I tested this with three different credit cards that belong to me personally — not anyone else’s cards — and the same thing happened. I’m trying to understand why this is happening.

Now I’m wondering: could using a CC checker trigger anti-fraud systems and cause cards to be flagged as high-risk? I’m honestly just trying to figure out why this is happening.