How can I use the API to move Cards from one Collection to another?

Hi everyone!
My team and I are doing a big organizational overhaul of our Guru instance that is going to involve changing up our collections, redoing our naming conventions, and setting up a new tagging system to make everything more scalable. I'm working on setting everything up so we can do this via the API when we're ready and am ALMOST there, but am running into some difficulties moving a card from one collection to another (with the API).
Here's the JSON I'm sending to the Cards endpoint:
```//create JSON
let json = {
"tags":tags,
"collection":{"id":collectionId},
"content": content,
"shareStatus":"TEAM",
"preferredPhrase":cardName
};```
`collectionId` is a string, and exists in Guru. I'm getting a 200 response back from my PUT request, but the collection assigned to the card remains unchanged (all of the other elements update as expected). Is this because the card is already assigned to a Collection and a Board?
Thanks for any pointers!