Ohaaa, we found a real logical issue in the market SDK haha
The reason is that your "accept" does not grant the market permission to handle your NFT beforehand. I will add that in the next version. Until then, you could put that NFT up for a listing - this route does grant the market permission to handle your NFT. After that, your "accept" will not fail anymore.

But maybe let us keep it that way so we can test the fix I am going to apply. Both would work fine for me :)