In my experience with saas/apps, they tend to trust our internal attribution. The way we did it was to have custom links for every influencer (
company.com/influencer) and tracked signups through there using our internal analytics. In some cases we've had to share screenshots/access with creators just to build that trust up.
I'm not sure how you'd use coupons for a consumer focused app (as most of them are freemium/no cc needed), so maybe link tracking is a good option to go with. Let me know!