A crawlable link is a link that can be followed by Google. Links not crawlable are therefore links with a bad URL, these links can be exploited by the JavaScript code of the page but not by crawlers. For Google to be able to track your links, they must use a <a> tag with the href attribute followed by relative or resolvable URLs (a real web address to which Googlebot can send queries).
Example 1 : crawlable link
<a href="https://example.com">
Example 2 : URLs that can be resolved
/products.php?id=123
https://example.com/stuff
It's important because only this format allows you to make your content available to Google's robots. Non searchable can be a problem since the robots will not know which page it should point to (the link) and will not index it (the destination page).
In order to solve a problem with a crawlable link you should :