I got a warning with membership plugin

To begin with I tried selecting the plugin option and trying to get this directed via that selection but when I select the site and try then to select the plugin no plugin pops up.

Ok now here is my issue I keep getting the following warning when I activate "Free Subscriptions" on my Membership Plugin

call_user_func_array() expects parameter 1 to be a valid callback, class 'freesubscriptions' does not have a method 'mytransactions' in /home/mojara/public_html/mojara4529/wp-includes/plugin.php on line 429

Can you tell me how to correct this.