Ignacio,
You can do this by editing the template: shop_coupon-edit.php
The template is located here: wp content/plugins/wcvendors-pro/templates/dashboard/shop_coupon-edit.php
Here s instructions on how to move & modify templates: https://www.wcvendors.com/kb/changing-vendor-templates/
You need to comment out approx. line 59, which looks like this:
<?php WCVendors_Pro_Coupon_Form::free_shipping( ( array_key_exists( 'free_shipping', $coupon_meta ) ) ? $coupon_meta[ 'free_shipping' ] : '' ); ?>
To comment out the line, do this:
<?php // WCVendors_Pro_Coupon_Form::free_shipping( ( array_key_exists( 'free_shipping', $coupon_meta ) ) ? $coupon_meta[ 'free_shipping' ] : '' ); ?>