Project is not associated with contract

Summary:

A contract was incorrectly created towards a project at project level:

I have reversed all revenue and removed the invoice from this contract. I'm unable to remove the project from the contract. I have therefore set the contract to status Closed.

My colleague has created a new contract and associated the line at task level:

However this is not taken any affect. The revenue is not created towards this new contract and I'm unable to find the project when I create an invoice event.

How can I make my new contract work with the prject (at task level)?

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