The defined api states
|content_id||integer||The issue or pull request id you want to associate with this card. You can use the List issues for a repository and List pull requests endpoints to find this id.
Note: Depending on whether you use the issue id or pull request id, you will need to specify Issue or PullRequest as the content_type.
However this does not work with the issue ids from the repositories. I expect they cant as they are not unique. How do I specify from what repository to to get the issue? As it is defined as an integer it leaves little room for the standard schmea of