That's strange, chromium+android should work fine. Could you try other browsers (Chrome? FF?) on the same device, please?
I’ve tried Brave and Kiwi as well. Same error. Also safari on ios doesn’t work with a different error. I’m using CalyxOS for Android.. maybe it’s related to that? I’ll try FF as well.
Same error with FF. When pressing the notification button the OS does popup the notification to ‘allow notifications’. When you press allow it still gives the same error in the browser.