It's true—when your contact lens prescription expires, you'll have to make an appointment with your optometrist in order to obtain an updated one. You won't be able to buy more contact lenses until you do, even if you buy them online.
Will LensCrafters take an expired prescription?
If you have a valid prescription you can always use it at LensCrafters, either online or in stores - no matter where you got it. Just be sure to check the expiration date, as entering an expired prescription may result in your online order being canceled.