Selfhosted app on Cloudflare - but now how to get custom domain to show?

I want my user to go to myexampleurl.com and have it redirect to a certain page on my cloudflare site (aka my self hosted weweb app site), BUT have them still be seeing myexampleurl.com.

I tried to set up a Cloudflare worker but it just wouldnt work, shows a black page only.

Does anyone know how to get this to work? So people can visit my weweb app from different custom domains (and have it show specific pages)

That is effectively what Coalias does, and they are also using cloudflare. When I took a look at how I could do it myself, I felt it was way above my skill to setup. So if you do figure it out, I’d love to know how to avoid paying for another app.