For your functions.php file or custom plugin:
// Increase number of meta fields shown in dropdown
add_filter('postmeta_form_limit', 'customfield_limit_increase');
function customfield_limit_increase($limit) {
$limit = 100;
return $limit;
}
Otherwise, the dropdown for Custom Fields is capped at 30 (alphabetically).
Before:

After:

Thanks for your post..
I needed this.. but I also need an addition to it.
Do you know if there is a way to filter out certain meta values from displaying in the drop down?
I have about 50 in my drop down but only 15 of them are actually viable for use in a “new order” admin
I would like to display only the valid order based fields.
Thanks for any assistance you can offer.
Thank you for this! I have bookmarked your website. I had to use another plugin called ACF. Now, with this that is not required also it was simple to add the code and get it right as I wanted. Also, if you can help me with Butch’s concern that would be great
This is not working for me. Has anything changed?
Hi there! And thank you so much for this, it has been so helpful. However, I now use a child theme and this function doesn’t seem to be working in it. Any suggestion?