Generally, you can pay for a PLUS subscription using a credit card, S€PA eBanking or SOFORT Überweisung.
If you choose to pay by credit card, you will automatically sign up for a recurring subscription. However, the automatic renewal can be cancelled at any time.
All other payment options are only available as one-time-payments, so your PLUS subscription won't automatically renew.
To purchase PLUS, please click your profile picture (top right) » 'Upgrade to PLUS' or 'PLUS Member' » 'Upgrade Now!' or 'Renew Membership' » then select your plan of either 1 year, 1 month or 3 months. If you want a subscription that automatically renews, you must pay by credit card. All other forms of payment can be used to purchase a one-time, non-recurring, subscription.
For an overview of your PLUS transactions click your profile picture » 'PLUS Member' (or 'Upgrade to PLUS' if you are currently not a PLUS subscriber) » then click 'Transaction history'.