Coinbase uses device confirmation, a security feature that requires all devices (mobile and computer) and IP addresses to be authorized before accessing your account. This process should only need to be completed once for each device or location.
Device confirmation troubleshooting differs from 2-step verification troubleshooting.
Authorize a new device
To authorize a new device or IP address:
Sign in to your Coinbase.com account.
An email is sent to your registered email address.
From the device that needs to be confirmed, select the button in the email to confirm.
You should be able to fully use your account.