Auto-renew is when your plan renews at the end of your plan cycle.
It's the default setting for all amaysim accounts and a hassle-free way to recharge your plan (You can switch auto-renew off at any point through My amaysim).
As a Prepaid customer we'll renew your plan by charging the balance to your selected payment method (e.g. a credit card, debit card or PayPal account) - if you have any amaysim credit in your account, we'll use that first and charge the remaining balance to your active payment method.