Are you a first-time user of curve, or are you already set up and have only just started to get this error? If first time, then please ensure you have followed all steps correctly to set up your account. If already set up, then what's changed? A recent update? Are you currently abroad? Have you reached out to Curve customer services to see if your account is okay and that the service is not currently experiencing an outage.
Try clearing the curve apps cache and data and try logging in again.
