One time I had a different issue, where WM pay just kept pending for like 10 minutes and I gave up. Not sure what happened, it was a small amount bought with something else on a phone+account+card that had worked before. Eventually the charge came off my card, not sure whether my random calls to customer service were necessary for that to happen or not. The time it failed was at human checkout using an old-style terminal. Let's call the WM with that bad experience "WM #1." I never tried using that same phone or that same WM again for VGC. I have successfully used SCO (no VGC) at WM #1 since then.

At WM #2, I've been able to buy nearly $500 VGC at a time (haven't tried more) with 2 other phones on WM Pay at the SCO.

At WM #3, I've been able to use 3 other phones on WM at the SCO (didn't try VGC).

I always keep my total purchase under 500 and include bananas or tea or something with my purchase. Not sure that's necessary. And that didn't help me the one time.

There are a few other DPs more like yours where WM pay just arbitarily declines. I'm probably about 4k deep into my VGC buys and that was over 6 months.