I had a lot of problems with getting Umami to work with Vercel, in the end I abandoned it and used Vercel Analytics.
First Umami was being blocked by all ad blockers and it caused my web app to crash, then I had to use some workaround which allowed it to work with ad blockers but stopped my Express app from sending responses back to the frontend.
It irritated me so much, because there is not enough documentation for it, although I did find multiple people reporting something similar like me. I just called quits on it, analytics shouldn't be that complex to setup if you are not self-hosting, the Vercel one is serving me okayish for now.
First Umami was being blocked by all ad blockers and it caused my web app to crash, then I had to use some workaround which allowed it to work with ad blockers but stopped my Express app from sending responses back to the frontend.
It irritated me so much, because there is not enough documentation for it, although I did find multiple people reporting something similar like me. I just called quits on it, analytics shouldn't be that complex to setup if you are not self-hosting, the Vercel one is serving me okayish for now.