The annual subscription of £20 is due each April for those paying by standing order, on the anniversary of your first payment if paying by PayPal or on joining the SOA (if part way through a year).
Most members, after joining and paying the first year subscription by bank transfer, set up a standing order. The form for that is here : SOA SORD FORM 2017-18
If you wish to renew your subscription by PayPal, the links are below.
PAY SUBSCRIPTION BY PAYPAL :