InvoiceItem:
      type: object
      properties:
        quantity:
          type: integer
          example: 1
        cost:
          type: number
          format: float
          example: 10.00
        product_key:
          type: string
          example: 'Product key'
        product_cost:
          type: number
          format: float
          example: 10.00
        notes:
          type: string
          example: 'Item notes'
        discount:
          type: number
          format: float
          example: 5.00
        is_amount_discount:
          type: boolean
          example: false
        tax_name1:
          type: string
          example: 'Tax name 1'
        tax_rate1:
          type: number
          format: float
          example: 10.00
        tax_name2:
          type: string
          example: 'Tax name 2'
        tax_rate2:
          type: number
          format: float
          example: 5.00
        tax_name3:
          type: string
          example: 'Tax name 3'
        tax_rate3:
          type: number
          format: float
          example: 3.00
        sort_id:
          type: string
          example: '0'
        line_total:
          type: number
          format: float
          example: 10.00
        gross_line_total:
          type: number
          format: float
          example: 15.00
        tax_amount:
          type: number
          format: float
          example: 1.00
        date:
          type: string
          format: date-time
          example: '2023-03-19T00:00:00Z'
        custom_value1:
          type: string
          example: 'Custom value 1'
        custom_value2:
          type: string
          example: 'Custom value 2'
        custom_value3:
          type: string
          example: 'Custom value 3'
        custom_value4:
          type: string
          example: 'Custom value 4'
        type_id:
          type: string
          example: '1'
          description: '1 = product, 2 = service, 3 unpaid gateway fee, 4 paid gateway fee, 5 late fee, 6 expense'