What specific scenario exemplifies insufficient 'consideration' in an agreement where both parties genuinely intended to create legal relations?

A specific scenario exemplifying insufficient 'consideration' in an agreement where both parties genuinely intended to create legal relations occurs when a party promises to perform an act they are already legally obligated to do under an existing contract, in exchange for a new promise of additional payment from the other party. In contract law, 'consideration' is a fundamental element, referring to something of value (a benefit to the promisor or a detriment to the promisee) that is exchanged between the parties. It is the 'price' for a promise, signifying a bargained-for exchange. 'Intent to create legal relations' is a separate contractual element, meaning the parties genuinely intended their agreement to be legally binding and enforceable by a court, rather than a mere social arrangement or a gift. For this scenario, we assume such intent is present. For example, consider a builder (Party A) who has a pre-existing, legally binding contract with a homeowner (Party B) to construct a specific extension for a fixed price. Halfway through the project, Party A encounters an unexpected increase in the cost of materials, which was not accounted for in the original contract. Party A then approaches Party B and states that they cannot complete the extension unless Party B agrees to pay an additional sum beyond the original fixed price. Party B, eager to have the extension finished by the agreed deadline and genuinely intending for this new arrangement to be legally binding, verbally agrees to pay the extra amount. Both parties genuinely believe this new agreement to be enforceable. However, despite their clear intent to create legal relations regarding the additional payment, the new agreement lacks sufficient consideration from Party A. Party A's 'promise' to complete the extension, which is the 'benefit' offered for Party B's promise of extra money, is something Party A was already legally obligated to do under the terms of the original contract. This is known as the 'pre-existing duty rule,' which states that performing an existing contractual duty owed to the promisor does not constitute fresh, new consideration for a new promise from that promisor. Since Party A is providing nothing new of value beyond their pre-existing obligation in exchange for Party B's new promise of additional payment, Party B's promise is considered gratuitous and unenforceable due to a lack of valid consideration flowing from Party A for that specific new promise. The agreement for the additional payment, despite the parties' genuine intent for it to be legally binding, fails as a contract because the essential element of new consideration from Party A is absent.