How do you figure out fair compensation when you bring on a partner in your business?

Hey all—
I’ve been somewhat of a lurker here but have been an avid listener of the podcast for a couple of years now.
Wondering if anyone has thoughts or experience with this—
I have a physical products business I’ve been working on for the past couple of years. I’ve struggled with the marketing/social media side until recently when I found a great fit in a friend / partner who owns a marketing firm to take on branding/marketing/social media. That is absolutely huge for me, as I can now focus on production and all the other aspects of the business.
We initially talked about making sure we both come to an agreement that we both feel is fair and we both feel good about, but now that it’s getting down to the brass tacks of figuring out what that looks like, I’m not sure what actually is fair. Do I give half of my business? Is it a much smaller percentage for a CMO type of partner?
I know that at the end of the day, we can design whatever kind of agreement that works for us. But I’m curious if anyone has thoughts about what is typically done in this scenario or if anyone else has experience with this.

Thanks y’all, happy Friday.