fix #2057

templates/repo/issue/view_content.tmpl

@@ -323,7 +323,7 @@
 	<div class="ui comment form">
 		<div class="ui top attached tabular menu">
 		  <a class="active write item">{{$.i18n.Tr "repo.release.write"}}</a>
-		  <a class="preview item" data-url="/api/v1/markdown" data-context="{{$.RepoLink}}">{{$.i18n.Tr "repo.release.preview"}}</a>
+		  <a class="preview item" data-url="{{AppSubUrl}}/api/v1/markdown" data-context="{{$.RepoLink}}">{{$.i18n.Tr "repo.release.preview"}}</a>
 		</div>
 		<div class="ui bottom attached active write tab segment">
 		  <textarea tabindex="1" id="content" name="content"></textarea>