First, please make sure you selected to 'Ship with Depop' - on your in app receipt if you see the button 'Mark as Shipped' this will mean that you have chosen to arrange your own shipping.
If you're unable to access your label due to a message prompting you to verify your PayPal account. Please head to PayPal and follow these steps here to verify your account.
Then, try force closing the Depop app and reopen it. Once you have done this, go to your sold item receipt and access your shipping label from here.
We do recommend you allow up to 48 hours whilst your PayPal account is being verified. If you're still receiving the same message and still aren't able to access your label after some time, please report this directly via the Depop app: Profile > Settings > Support > Need help > Technical issues > I've still got an issue with both your @username's and the date of transaction.