How to allow free listing submissions and charge only for listing upgrades
If you want your users to submit listings for free but charge them for additional features like making the listing Featured, adding additional custom fields, ..., it is still required that you create a base plan because upgrade plans are not available if a base plan is not applied to a listing.
In this case you must create only one base plan and select Free or Trial as Payment type.
Make the plan default, and if you set Show in submit form to No, users will not see the plan when submitting a listing, but this free plan will be processed automatically.
This will make it possible for listing owners to Order Upgrade and pay only for special features that you created as listing upgrades.
If you have existing listings that were created before listing plans existed, you will need to use bulk order generator to apply the base free listing plan to all of them.