Hello,
From what I can tell the code looks fine.
If the vendor has entered the value for the field using the front end store settings, then the value will be shown int he admin store settings– it does not need to be filled in. If the vendor needs to edit it, they can visit the front end form to do so…
You can use the template page to place the script needed to show on that page:
wp content/plugins/wcvendors/templates/dashboard/settings/settings.php
There are also hooks available on that page to use for placing actions you have written, such as:
wcvendors_settings_after_paypal
wcvendors_settings_before_paypal
wcvendors_settings_after_shop_name
and more..