Data connection syntax issue - changing to URL

Hello, 

I have had a connection set up in Power query (for PowerBI) which previously was set up via a file path. However, we're now transitioning the data connection to come through a service account which has meant we need to switch the connection to web based so connect via sharepoint to update the gateway.

However, when we've tried to do this, it came up with a Token Literal expeted error which I understand as an issue with the syntax. 

This is the current syntax:

=Excel.Workbook(Web.Contents("URL Address"), null, true)

I've also had another error come up "couldn't authenticate credentials".

Any ideas? Thanks in advance!!