when your site is set up for ppl earn credits with user credits plugin and use them to upgrade there accounts with credit points 
the wording is bit messed up and is confuse users into thinking they are going to be charged to upgrade 

in admin setting can you put a tick box for use credits
and make it change the language values 
from
{$price} {$currency} per {$period} days (recurring)
to
{$credits} per {$period} days (recurring)

same for none recuring

maybe hook {$credits} to a value in user credits plugin 

i dont know i use payment by user credits plugin and  its just not right 

and i dont think theres a way that plugin could fix this problem