Gift cards can now be sold from your site and customers can choose the amount. You can give them options to pick between a range using 'Custom' in addition to choosing from preset amounts.
To do this click Settings > Bookings > Gift cards creation
Choose to allow customers to create their own, how long the cards will last, whether to allow customers to pick within a range and/or some pre-populated options.
Click Apply Changes, the, preview the link up top to see what the customer will see. Consider using this link on your site outside Momence for higher traffic.