If you are in business development and partnerships, at one point you’ll have to sell something that isn’t fully built yet. This typically happens in the earliest stages of a company, as well as in new product cycles.
I’ve seen the most success in selling something that isn’t ready when it is less about selling and more about information gathering. Your company is considering building a product or feature- you go out and talk to many clients/partners for said product/feature. If you get enough interest in it- you build it. As companies give you feedback on it (maybe you have a prototype, maybe you have a deck, maybe you just talk about it conceptually) you continue to take feedback and bake it into your ongoing selling process. For example, if you meet with company X at 1pm and they give you a great idea for a feature in the product, when you meet with company Y at 4pm, you should bring it up and get there take on it.
Bottom line: Selling something that isn’t ready yet isn’t easy, but if you strike the proper balance you can garner some early interest to capitalize on once your product is ready.