Parse error on sitemap.xml page

I try to add the sitemap page to robots.txt so Google can easily find it,
When checking the page first by browsing to https://mysite.com/sitemap.xml I get the following error:

This page contains the following errors:
error on line 1 at column 8: XML declaration allowed only at the start of the document

Shouldn't this show an XML output? I want to be sure that Google uses my sitemap properly before adding it to robots.txt

Yes it should be HTML output. I just tested on my local and it appears correct. Is it possible to get the real live URL of your site?

Sorry for the delay (busy times). The URL is https://electronicsworkbench.io/sitemap.xml. Meanwhile I just imported the sitemap to Google Analytics anyway and it didn't complain...