Changes to List all fixed charges for a plan

the response property fixed_charges/items/invoice_display_name became nullable for the status 200

the fixed_charges/items/units response's property type changed from number to string for status 200

added the optional property fixed_charges/items/taxes/items/applied_to_billing_entities_codes to the response with the 200 status

the response property fixed_charges/items/taxes/items/description became required for the status 200

endpoint added