Are relations not created automatically?

Quick question. I have 2 content types


An Auction has many Bids.
A Bid has one Auction.

I POST to Bid and link it to an Auction. That works as expected. The Auction shows up properly in the Bid relation field.

However, the Bid doesn’t show up in the Bid relation field for the Auction.

Do I need to manually create the Auction to Bid relation with a PUT to /auctions/:auctionId??