Can logon fine using browser but Android app throwing same error. I'd hazard a guess they have some anti-fraud system in use thats being over sensitive to different devices / browsers.

Whats the best way to contact Delta support for tech issues?

Edit:
Yeh, looks like Delta use Accertify, who are likely blocking the sign in attempts. Will need DL customer service to take action to allow another device / app type based on my experience of Accertify. https://www.accertify.com/delta-exte...prevent-fraud/