Who issued the cert?
What are the full T&Cs?
For an award flight, the earnings are based on the cost (in miles)?
What does the cert state its value is? (likely in T&Cs)?

My first order guess is this is a UA promo with no "value"., no earnings -- but have never seen this before so it is a pure guess
Note if it has value you will need to pay taxes on the value. Even if miles.