Web API method to remove or clear promo code

Preliminary Information:
- Tessitura Version: 12.5
- We are not using TNew, our website is completely custom. I am the web developer and I built the whole website myself. 

What is the proper web api method to clear or remove a promo code on the web? I had been using the UpdateLoginWithPromoCode method and simply using the default source code of 0 (zero), but that seems to causing issues with the session for some reason. I have tried to use the UpdateSourceCode method but that doesn't seem to work with a source code of 0 (zero). 

Thanks in advance!



[edited by: Chip Hunt at 11:27 PM (GMT -6) on 12 Sep 2016]