Fusion scenario to add tasks to a project and add predecessors to each other within the same project?

Hi Community,

I am trying to find a way to add after a specific request has been created a task list(three records) to a project via Fusion. So far so good. Depending on the individual request I created three records to the project. Where I am stuck is defining the predecessors. I could only find the API call that is referring to predecessors across projects, but since these tasks are not in the project, yet, they also do not have a task number, that I could refer to as the predecessor. So the API call

Url: TASK/{ID of task}

Method: PUT

Body: {"predecessorExpression": "{{Number of task}}"} - doesn't make sense since I do not have the number.

I tried to add in the Body section: {"predecessorExpression": "{{ID of task}}"} - since it is the newly created task before, but I receive an error message: [400] APIModel V20_0 does not support action %XXXXXXXXX%XX (TASK)

Any workarounds for this?

Thanks for any advice in advance!