Need help on Sharepoint query search building

Hi,

I am trying to integration Servicenow with Sharepoint to find the files available in Sharepoint Sites which i acheived using "https://graph.microsoft.com/v1.0/drives/drive-id/root/search(q='sharepoint')" & it is working perfectly fine but it is working only for specific drive/site.

Now the requirement is when user search with a query word it should search in all the sites available in our Sharepoint and give the response after lots of googling i found an article that i thought suits to me :  SharePoint Rest API.

When i try with the given ex: GET http://mydev.sharepoint.com/_api/search/query?querytext='sharepoint' in Graph API explorer it is not even the running and i am not able to see any response. Later the tried the same by giving the End point URI in Servicenow and i am getting Invalid User & Passworkd & Response: 401.

Note: My Servicenow instance is already configured with oAuth and it is working for specific Drive search but when i am trying with Sharepoint rest api search i am getting authentication issue do i need to proceed with other Authentication method ?