You can advertise your chat on xats with a 728x90 banner.
Create a banner image, upload it to TinyPic or Imgur and go to the promotion page: https://xath.hu/store#!promotion.
If it is the first time your banner has been used, you will need to queue it for authorization, which costs 50 xatss. After approval, you will be emailed and can start running ads for your group.
The current maximum advertising time is 6 hours, while the minimum is 30 minutes. Prices can be found by clicking the 'Get cost' button.
User ads are allotted 50% of ad space and will start running within one minute (may vary due to caching).