To ensure that you can access the Securly admin console without error, it is essential to add Securly as an App in your API control in G Suite.
For this, you would need to log in to your Google admin console and navigate to Security > API controls and click 'Manage Third-Party App Access'.
Now select 'OAuth App Name or Client ID' from the dropdown for 'Add app'.
Search for 'Securly' and select the radio button for 'Securly' from the list displayed.
Click 'Add' and you are done.