Log in to https://cosy.erc.edu/en/login and click the link "Membership" in the menu on the left hand side.
On the next page you can read about what the membership entails and what benifits it offers.
At the bottom of that page you have the option to add a discount code (If you have one) and to order your membership.
The next step is to confirm your billing address. Your addresses will be shown on this screen.
Click the tick beside the address you wish to use as your billing address, or add a new address.
If you would like to have a certain reference on your invoice you can add this on the next page. (For example a Purchase Order number)
Follow the steps on the screen to complete your payment.