I did read what you wrote. You wrote that potlucks are the norm for your area. You did not write that it was normal to charge for a party. Other people came along and said that it might be normal in your country, but I don't have the habit of believing a "maybe" from another poster over a definite description from the actual OP. I always like to wait for the actual OP to confirm before changing my answer. And you said potlucks were the norm.
If that wording is indeed what you wrote in the invitation, then yes your intentions to collect money were clear. However, you wrote something quite different in a previous post that was definitely open to interpretation. I understand you were probably just paraphrasing at the time, but we aren't mind readers and we were answering based on what YOU posted. In your previous wording, it sounded much less clear that you were expecting a definite payment from each guest and not just a suggested amount that was optional.
In any event, no matter how clear you were, you have had trouble 2 prior years in actually collecting the money. That to me says that this is not working, regardless of it being culturally acceptable.