The Update a repository API endpoint can be used to update the properties of a given repository.

However, it's currently not possible to change/update the parent of a forked repository using that endpoint. When providing a value to the parent field, the value does not persist :

curl -X PUT  -u username:app_password "https://api.bitbucket.org/2.0/repositories/<workspace>/<repository>"
-d '{
"parent": {
        "type": "repository",
        "full_name": "workspace/repo_slug",
        "name": "repo_slug",
        "uuid": "{REPO_UUID}"
    }
}'

This feature request is to implement the ability to add/update the parent of a repository using the Update a repository API.