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.

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.