One of the Campaigns you can create at Flingah is a Competition, where you can choose an amount of customers to be automatic winners i.e. The first 5 or the first 20 are winners.
First X Number is therefore the number of winners you want for this competition. If you enter First X Number as 5, the first 5 customers to text your keyword will be considered a "winner", and they will receive your Successful Message as a reply. Enter the number in the corresponding field.