By the way, if you just see a "Thank You" page when you follow that link, then the system thinks you're already a subscriber. This is probably because you contributed a one-off payment back in the early days, which at the time made you a subscriber according to how the system worked before PayPal's recurring payments were integrated into the software. Your profile page might be showing your subscription as 'cancelled', which I think happened automatically when the subscription integration was upgraded.

So if you want to contribute more money and all you see is the "Thank You" page, just send me a message to let me know and I'll remove you from the Subscribers user group, after which you'll be able to revisit the link and subscribe (which will put you back in the Subscribers group with an active subscription).