In one of projects, the customer is trying to include the vendor selection as part of the fixed cost project. While the scope of the fixed cost project clearly says to work with "an external system that provides xyz functionality", nowhere does it say that the project includes finding the said external system/vendor. [To be fair, it doesn't explicitly exclude it either.] In fact the scope document defines the draft API that would exist with this external system, and also states that the actual API may differ to some extent, and we are comfortable with that variability. But the process of finding this vendor/system is a subproject that is just as significant as the entire project itself.
Any suggestions on how typically this is worded and the scope can be refined/adjusted now? More than the cost of extra hours, we are concerned about the extra calendar time that it will take and will entirely push this project into red for us.