Are you being asked to verify your card in Libby?  Here's what to do. Follow the numbered steps below:

 Click the Libby menu that looks like 3 lines, then Manage Cards:

Click "Actions":

 Click "Verify Card"

 Type in the whole barcode number from the back of your library card. Do not add any spaces or dashes. Then click "Sign in".

You should get a message that your card has been verified. 

Pro Tip! You may be prompted to do this mid-task, say, while checking out a hold. If that happens, go back to the menu (remember-the 3 lines) and go through the steps exactly as explained above (INSTEAD of only entering in the library card number when prompted - this has sometimes produced errors.)