Rejections and blocks in gambling advertising will always happen; it is inevitable.
First and foremost, the blocking occurs because of your landing page—whether it’s an app, a PWA, or direct links.
Use cloaking and a "white page" that is thematically similar to the creative in your ad.
It is also important to have high-quality accounts, as the moderation process depends on account quality as well.
Using slot machine imagery in your creatives is quite feasible; the knack for it comes with experience.