First make your site professional, add some pages like faq and a professional homepage. Right now every visitors are striking on login page and site doesnt have any kind of content.
After you will redesign your site make professional looking ann thread for your betting platform with all the feature your platform have.
Now spend some money in advertising, provide high class support to players and try to offer good affiliate commision.
This is true, remember that people needs to see a nice website, they will deposit money on it so make it at least attractive. When I went to the website it is made out of a template of website builder program. Of course as mostly suggested you also need to spend in advertising, but besides the social media and other online advertisements you may do the offline advertisement. Spread it locally.