Is your site suspended? If your site doesn't violate the URL rules, it is most likely because the website you are adding doesn't work in frames. You can test if your site will displayed with this link checker tool. It could also be that the site is http. For example, perhaps you added a https tracker URL but your original link in the tracker is http.
If your website doesn't work in frames (such as social media or Youtube links), it will be suspended because you would be wasting your credits advertising it. If you can't see the site in the site checker when you add it, no one else can either and there is no point in advertising the link. However, you can make your own ad for it in the Page Creator or in any splashpage maker.
If the traffic exchange picks up on something that could be a problem while your site is being advertised, it may automatically go into "Suspended" status to keep surfing clean and smooth. For example, the suspended website could be down or have some sort of technical issue. If this happens, just delete it and add it again when it's been fixed. If this happens, it will not say for what reason your site was suspended.
Sometimes sites that have been previously approved get suspended also. It may seem random, but the traffic exchange script runs through all the sites now and then to check them for anything that could be a problem. This is done to ensure surfing is clean and smooth.
If your site is suspended because it broke the site terms, it will not be activated and you will see a reason why it was suspended. Credits have been returned to your account and the site will eventually be deleted. Sites on expired domains will also be deleted.
Click here to see a full list of the currently banned sites and the reason why if they are banned.
Related articles:
URL Rules
Banned sites list
Add a website