Question about selling post individually.

I've made about a post before asking how to sell individual post. The answer I got is the feature is not available for everyone. So my questions are.

1. Those who are able to do it, how did you unlock it? Is it relate to how long you had your creator account or the number of members you have?

2. Also, is it viable to do paid per post strategy and just skip the monthly subscription method entirely? The reason is I get too busy some week to post consistantly and I feels bad when that happen. I rather just let people buy what they want when I post rather than committing to be charge monthly.