In order to allow for campaigns with only Free Products to be ordered, what you'll need to do is the following:
- Use the ats_managed value for paymentMethod
- When a campaign has a payment value of 0, instead of using the wallet you will need to switch the paymentMethod to ats_managed
- When a campaign has a payment value greater than zero, you should continue to use the wallet paymentMethod as you have it setup now
- Check out the schema here.