Operations for add-ons when retaining existing modifications.
Add-ons to add (by template ID).
Add-ons to edit (by template ID; server resolves to instance).
remove[ID!]IDs of add-on instances to remove.
input RecurringBillingSubscriptionRetainExistingAddOnsInput {
add: [RecurringBillingSubscriptionAddOnInput!]
edit: [RecurringBillingSubscriptionAddOnInput!]
remove: [ID!]
}