There is no set check list that will correctly determine if your idea is valid or not.
Often the best ideas are at first simply crazy. Think of Airbnb, staying in a strangers home, or Uber riding in a strangers car.
Validating an idea is a difficult unpredictable process.
Some questions that can be helpful are:
What is the customer trying to accomplish?
What is the ideal experience for them to accomplish what they want?
What has changed in the past three years that makes now a good time to provide this solution?
How does the solution you have not help the customer accomplish what they want?
Try to find everything wrong with your solution, ask your customers what do you hate about this?
And if the negatives don’t outweigh the pros then your idea is a little closer to being validated.