Gambling advertising on social media and fines

I often see casino ads from bloggers on Instagram and YouTube. I read that huge fines can be imposed for this, even on the bloggers themselves, if the advertising does not comply with the law. I'm interested: if I promote gambling advertising on my social networks or even sign up for an affiliate program with an online casino, what specific requirements must be met to avoid a fine? How can one understand what makes such advertising legal, and what can lead to millions in fines?