We're sharing 25% house edge with advertisers, and it can be both negative or positive. We don't always get money, but overall house is always in profit.
You can have negative balance on your account and you don't owe nothing, but it can happen in some cases.
By sharing your referer link you become our partner. Your investment is sharing your referer id. We take care of the rest.
We are avare of this issue and it will be fixed in new version.