Great product value propositions ALWAYS start with the customer problem being solved, specific benefits, and the ideal customer.

In a right-side-up world, you would have begun your product development using this same framework. What is the <core problem> my <target customer segment> is experiencing, and how do we <solve> it <better than anyone> else? If you've done that, then writing out a value prop is essentially putting words around what you've built.

If you didn't start that way, and now you're attempting to shoehorn a value prop back onto an already created product, then you'll need to unpack your product and discover the answers to the elements above. Start with what is the core problem we fixed? Who is our ideal market / customer? Etc.

Be VERY careful to: avoid buzzwords, avoid droning on and on, never list features, don't speak from your perspective, and be sure to use language your target audience would use.

Your value prop, in it's essence, should be similar to something your ideal customer would say about themselves. Ex: I feel like a spreadsheet superhero when I use Airtable! I hope my boss doesn't find out how easy this is. ;^P

Some great resources for figuring out your value prop messaging:
https://www.wordstream.com/blog/ws/2016/04/27/value-proposition-examples
https://conversionxl.com/blog/value-proposition-examples-how-to-create/
https://optinmonster.com/32-value-propositions-that-are-impossible-to-resist/

I've been a PM or founder for over two decades. If you want help with your value proposition, unpacking your product to reverse engineer one, or you're just starting out and want to get it right from day one then give me a call. I'm happy to help!