This is a shop button for the BlueLine theme.
Code modifications:Open Themes/BlueLine/Index.template.phpFind:
// The [calendar]!
if ($context['allow_calendar'])
echo '
<a href="', $scripturl, '?action=calendar">' . $txt['calendar24'] . '</a>', $context['menu_separator'];
Add after:
// The shop
echo '
<a href="', $scripturl, '?action=shop">Shop</a>', $context['menu_separator'];
Then, your shop button should be working