I came here to ask the same questions. My IAP's were working when my app got approved a few days ago, but now they're failing. I'm getting code 21007 when I try to verify my receipts, and I'm getting this error on both endpoints, which shouldn't be possible.
ATCraiger
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As of now, it's working for me.
However, because of this and Apple's apparent lack of communication, we'll be implementing our own backup system, independent of receipt validation.