You are the project manager of a project executing work under a contract signed with a buyer organization. Just after the project has started, you notice that the buyer organization had made a mistake in the financial terms, and your organization stands to benefit considerably from this oversight. What should your stance be?

Do not take any action since a contract is a binding and legal document.

Discuss with your management how you could gain a bonus due to the increased revenue your company stands to gain.
Informally check with your counterpart in the buyer organization to see whether he or she noticed this error.
Bring the error to the notice of the buyer organization and have an amendment made to the contract since this was in good faith.