unable to set up a new data source on a gateway

Hi,

I'm trying to add a data source to my gateway.

I am trying to connect to a db which is on one of our organization servers (I have access to it).

Usually, when I log in to the server using SSMS, I don't need to enter a password, it authenticates me using my windows ID.

When I was asked to enter username and password in the data source setting page, I put in my username with the domain name (domain\username). As for the password,  I wasn't sure which password to use. I tried to use my windows password or my PBI password but it still doesn't work. That's the error I'm getting:

Please help