In contracts and more specifically in the topic of remedies, when the plaintiff has conferred a benefit to the defendant (unjust enrichment) and the plaintiff is seeking restitution, does the plaintiff have to file for rescission of the contract first before asking for restitution? let's say A hired B to do landscape in her garden, when A had done half of the work B repudiates the contract and refuses to pay anything to B.

In order to get the monetary value that B conferred to A under a restitution theory, does B have to sue for rescission first? or can he directly ask for restitution? does it change the answer if the contract was enforceable or not?