1. Your friends should register within the 2 hours after they have clicked the link and then enter the game within that period.
2. They need to install the game via specific megacool (mgcl.co) URL that you are sending them. If they install it via other means, it won't work.
3. They need to be new players. If they had the game installed on their device before, it wouldn't count.
Probably, your friends either didn’t meet this condition, used the wrong link, or accessed the link from their other devices (i.e. they needed to get the link on phone A, install the game on phone A, and do this within 2 hours of clicking the link on the same phone A).
Please try doing this step-by-step with one of your friends again, and if the counter has not increased then, please, contact us and include your friends' player IDs (looks like John#12345).