If the sweepstakes are unavailable in specific regions, then don't advertise the sweepstakes in those regions.
It's so annoying and frustrating to want to join a sweepstake advertised as being open worldwide, only to find out later (when you click on the links or banners) that this is not the case.
Most of the sweepstakes are only open to residents of the United States, Canada, the United Kingdom, Australia, and New Zealand. Just advertise the sweepstakes in these countries only. At the very least, specify these countries on the banner for the sweepstakes itself. Prevent those who are not eligible from clicking on the links or banners.
If possible, it is better not to advertise the sweepstakes to those who are not eligible.