In the old program Geoff Jowett said that any coke Zero product was fine also Pepsi Max, Sprite Zero etc, because the main enemy was sugar. However, this new program mentions nothing “packaged” including all soft drinks, sugar free or not.
I found when I first started the old program, especially in the first 3 day detox phase, I had to drink so much water that I really couldn’t fit any other drink in anyway.
I wouldn’t stress if you have one here or there, (in my opinion only, you don’t want to deprive yourself) but perhaps try get your water in first then see how you feel after that. 2-3L per day is recommended!