SEO - Document doesn't have a valid hreflang

Provide the steps to reproduce

1. Go to https://lighthouse-dot-webdotdevsite.appspot.com//lh/html?url=https%3A%2F%2Fnrn-v2-mst-aptd-at-lcz-sty-c1-mgu1yndpx-unly-oss.vercel.app%2Fen%3FnoAutoPreviewMode%3Dtrue

What is the current behavior?

SEO error with Document doesn't have a valid hreflang but there are only 3 and all seem to follow the spec.

What is the expected behavior?

I checked several times and even read https://hreflang.org/what-is-a-valid-hreflang/ and can’t figure out what’s wrong. The error is too wide to be actionable.

[patrickhulce]

The SEO category is not just for what can work according to HTML spec, but about SEO best practices. I find that Stack Overflow answer rather misleading as the source article is specifically calling out the use of relative href as a common source of mistakes, not saying it should be used.

The official search documentation on this subject specifically recommends use of absolute URLs for all hreflang alternates.

Alternate URLs must be fully-qualified, including the transport method (http/https), so: https://example.com/foo, not //example.com/foo or /foo

Until told otherwise by search, that’s what the audit will respect.

[connorjclark]

The error is below each item: “Relative href value”. You need to use absolute URLs.

Why do we check that in this audit? I’m not sure. Does anyone know?

Our docs don’t mention it either. https://web.dev/hreflang/

The string could be better.