sequence item 1: expected str instance, property found

Question

I am working Django app and I came cross where I need to extract a value of booking and pass it to another function to print a pdf doc with some details fields including a total amount of the booking

## defe function to extract deal total amount and to avoid circular import
@property
def extract_deal_total_amount():
    from sook_contact.signals import on_loading_booking_deal
    deal_values = on_loading_booking_deal('8388945051')
    convert_to_float = float(deal_values['amount']) * 1.20
    return str(convert_to_float)


// the in another function
    elif field_name == OccupationLicenseFieldType.BOOKING_FEE.value:
        return extract_deal_total_amount