Does your target market want your solution?
Do they acknowledge it creates value for them?
Are they willing to pay for it?
What words and phrases do they use to describe the problem you fix in their niche?
Another important area to consider, especially when you have an idea without any users would be, letters of intent.
While these letters of intent don't truly have a value it puts a measurable, trackable list of people that are willing to adopt your product, which may not be released and will softly commit to adopting to your service prior to you having it available.
While it's just a soft commitment it speaks louder than not having any paying customers on board.
For a pitch when speaking with investor and having letters of intent it gives more leverage.
Look into it and see how letters of intent to use your product is a great springboard when you may have no active users at the current time.