Why am I getting “Liquid syntax error: Unknown tag”?

That error, e.g. Liquid syntax error: Unknown tag ‘endif’, almost always means the block tags do not match up. A common cause is a stray {% endif %} with no opening {% if %}, an {% endfor %} closing the wrong loop, or a typo in the tag name. We walk the template, fix the nesting so every open tag has a matching close, and re-validate the whole file so the parser stops complaining.