Getting the error as detailed below, is most likely due to your currency configuration which is incorrect and the amount is therefore coming through as 0.00.
Our module requires that you use ZAR as your primary currency and that it is configured with the official currency code ZAR (not ZA or some other variation).
Modify this through the Zen Cart admin console on the Localization > Currencies page. Ensure that you have an entry with the following details:
- Currency = South African Rand (Default)
- Code = ZAR
- Value = 1.00000000