[[membership_only]] shortcode not working in membership plugin

Hi,

I have created some content that is viewable to different levels

[level-visitors]visitor[/level-visitors] works just fine

however,
[[membership_only]] text here [[/membership_only]]

does not work (shortcodes print in html output to non-logged in user) and additionally, the [[membership_only]] shortcode does not show up in the options>content protection tab. (whereas the [level-visitors] does.

How do I get the [[membership_only]] shortcode to work.

thanks,

PoU
my question is as follows: on