A thesis memo is the thesis written as a buying document: the bet the company is placing, why, and under what conditions it succeeds or fails. It stands in for the RFP checklist on the part of the decision nobody can specify in advance. Write one here for a deal you are working. Everything stays in this browser: nothing you type is sent anywhere.
There is one honest warning. You cannot write this memo for the buyer and hand it over, or it becomes your pitch on their letterhead. Offer the structure, argue over the theses, draft lines when asked, and let the champion and the committee own the words.