The buyer-facing promise. Positioning is the frame behind it.
A value proposition is one or two sentences that tell a specific buyer why your offer solves a costly problem better than the alternative they already have. It has to pass relevance, credibility, and differentiation. If it only sounds good in a brand workshop, it is not done.
Positioning is internal and names the category. The value proposition is external and names the outcome. Fill positioning first, then write the promise.
One sentence is the target. Two for a complex B2B offer. Longer is a paragraph you have not edited.