Office 365 Syndication application instance returns the following error on attempt to use the
Test connection button:
Cannot execute 'Test connection'. Сheck parameters of application instance and application endpoint configuration and try again. Request: http://www.microsoftonline.com/MOSI/1/0/action/Ping
The following application instance properties are mandatory:
ID of Native Client for Partner Center SDK
ID of Native Client for Azure AD Graph API
But they cannot be specified for Syndication application instance since Syndication Partner Scenario reached its end of live on the Microsoft side and not supported by Office 365 Development team.
Do not use Syndication application instances, switch to CSP Partner Scenario.