What's a smart way to collab with other SaaS? (communist but not communist)

I'm building a SaaS doing email

Every SaaS company needs email, whether they go with me, Mailchimp, Customer .io etc

I've also got many friends with SaaS companies

Any of you ever discover a way to collab or "exchange" customers? With an affiliate program ofc, so that each of us (me and the friend) get $$ when a customer buys

The way I see it:

• If it's a "benefits" section with discounts - it could look cheap; Plus I think it becomes kind of like credit card benefits where there are so many and benefits are so little that you feel overwhelmed and just don't read.
• If they integrate us within the app (which is a big ask) it's too intrusive. Feels like an ad?
• Other suggested we do that in onboarding - yuck. Onboarding edition is anyway so precious so I don't think anyone would ever want that.
• Any idea?