Thanks for the link!
It downloads a 1k file each time it opens. And then adds a "boost" to the upgrade screen if it gets that data. If it doesn't download the boost simply doesn't appear.
The file contains information on what platforms the promo game is available on and links (relative to my server) of screen shots for the promo game. If the promo key has changed since the last time you played, or you don't have the images, it downloads those images and stores them in the appdata path (around 700KB)
When it shows the ad, there is a big button on the bottom "back to game" so you don't need to look at it for anytime at all. It has a store buttons for steam, itchio, gog, and epic that show if the game if available on each service (or coming soon, early access, etc...) you can click on to go to the store pages.
The level of the boost can be adjusted by the downloaded file, I have it set to 35%. The boost lasts until the user exits the game. I can disable or enable the promo at will by altering the file.
Here's what's in the downloaded file:
steam|string|app/2363000/Apocalypse_Run
itchioDev|string|neurowocky
itchioGame|string|
gog|string|
epic|string|
statusSteam|int|5
statusItchio|int|3
statusGOG|int|0
statusEpic|int|0
logo|string|PromoApocRunLogo.png
fullpage|string|PromoApocRunFullpage.jpg
banner|string|PromoApocRunBanner.jpg
title|string|Apocalypse Run!
callToAction|string|Run for your life!
promoPitch|string|See a screen from my new game
blurb|string|Free demo of my new Strategy-RPG
text|string|In this Roguelike Strategy RPG, You'll stop the Apocalypse...\nIf Motorlord Dysentery doesn't get you first!\n\nFree Demo coming to Itch.IO
promoKey|string|ApocRunBh
promoValue|float|1.35
promoEnabled|int|1