Contract validation error - You can't associate this project and task to this contract line

Summary:

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Created a new contract, Added Line 1 and line 2, associated project and task to these lines. Getting below validation error.

You can't associate this project and task to this contract line.

A project and task in the same branch but at another level of the task hierarchy is already associated with a contract line. You must select a project and task from a different branch, or from the same level of the same branch of the task hierarchy.

Project WBS is as below.

Task 1 (associated with contract line 1)

Task 2 --> Task 2.1, task 2.2 (associated with contract line 2), task 2.3