Membership Pro 2 - sandbox paypal pending - but not completing

Hi there,
Membership seems to be working well enough when I create a member within WP, however following the process through via paypal sandbox the membership account reads that payment is 'pending'.
I've tested payment through sandbox a couple of times the paypal user account reads that payment has been made however WP / Membership Pro 2 isn't updating.
Anyone else had this issue? Solutions?
K