Paypal subscription option not showing when customer invoiced?

[northshore]

I have a monthly product set up for recurring payments in WHMCS but they do not get a paypal subscription link when logging in to pay the bill. Instead it's a plain old paypal link for a one off payment that they must complete each month.

In the billable item details invoice action is down as 'Recur Every 1 Months times'.

What have I overlooked?

EDIT: Also, when the customer paid for last month's bill via paypal (but using a different email than his email address on WHMCS - does that make a difference?) the system did not mark it as paid despite me receiving confirmation for the money in my paypal account. What would be the reason for that, should WHMCS not see this completed transaction from paypal too?

Further Edit: I checked paypal and the IPN was sent with HTTP response code 200 so it appeared WHMCS received word fine. Still didn't mark invoice as paid though.