Has a link with whitespace in href attribute issue means tha the URL contains at least one outgoing anchor link which has trailing or leading whitespace character in the href attribute.
Why is this important?
Leading or trailing whitespace in an href attribute is typically a CMS or user error. However, since they will usually get trimmed by browsers, they can be hard to spot.
Whitespace in href atrributes may cause a loss or dissipation of link equity, if search engines treat the link targets as distinct URLs.
How to fix?
Identify the anchors which have whitespace in the href attribute, and correct each one on a case-by-case basis – which may require reviewing the code that generates the links.
Depending on the specific issue, you may be able to fix a number of pages at once, if the problematic link is used in a template for lots of pages on the website.
Analyze not only pages having a link with whitespace in href attribute but the entire site!
Make a full audit to find out and fix your technical SEO in order to improve your SERP results.