The payment method I'm using for pixiv Premium has expired – pixiv Help Center

If you have a credit card on file
If you accidentally delete your registered credit card or it otherwise expires, you'll need to update your payment method for pixiv Premium within 24 hours of your next billing cycle to continue using Premium smoothly.

If you do not set a valid payment method within 24 hours of your next billing cycle for Premium, your membership will automatically be canceled.
If you have PayPal, Google Play, or the App store as your payment method
If you canceled your affiliated PayPal, Google Play, or App store account, your next billing cycle for pixiv Premium will fail and your membership will automatically be canceled.

If you would like to continue using Premium, you'll need to add another valid payment method after your membership is canceled.