Error in members Failed to sign up, please try again

Latest ghost install from digital ocean
Debug Information:
OS: Ubuntu, v18.04.4 LTS
Node Version: v12.18.0
Ghost Version: 3.39.0
Ghost-CLI Version: 1.15.2
Environment: production
When I try to signup it gives the error " Failed to sign up, please try again Members "
try here : https://neurologicaldisorders.co
these are the setting inside my ghost Labs