We have an electronic confirmation that the ad has played. To give you a bit of explanation; The billboard ads work like a slide show, the number of ads in a loop is dependent of how the media owners have set it up. For simplicity sake if we assume that there are 10 ads in a single loop. If the media owner is only able to fill the 9 slots, then the 10th slot is up for grabs. The screen will ping CAASie to see if we have an ad to fill that vacancy. If your ad is ready to play on that upcoming vacancy then it get delivered to the screen. Once the ad gets delivered and displayed on the billboard we get a notification that the ad has been delivered. This is the confirmation that we get, and once we get this confirmation then we take the cost of that play from your wallet.
So the digital confirmation is the proof of play. This is what you see on the dashboard as "The number of plays"