You need to do this yourself.
48 can't unilaterally initiate payments on your card other than via Continuous Payment Authority if you choose to use the auto-renewal option.
You can buy a membership plan here:
If you want you can enable membership plan auto-renewal here:
If membership plan auto-renewal ever falls for some reason then you need to buy your next plan manually before auto-renewal takes over again next time.
If you need to contact 48 support about this then see the links in my signature below.
