Credentials for the SQL Server Agent are invalid [2018]

I'm currently trying to build a small PowerApps application, mainly to mess around with it and learn what it can do. I have a gateway on my desktop that PowerApps has connected to, but whenever I try and create a connection I get the following error: Credentials are missing or not valid. inner exception: The credentials provided for the SQL source are invalid.

SQL Server Name > DESKTOPNAME\PRAVDA
SQL Database Name > Planner
Authentication Type > Windows
Username > DESKTOPNAME\MyWindowsUsername
Password > My windows password
Gateway > The correct gateway

I'm not sure why it's refusing to connect.

So far I have:

Added SQL Server to my firewall exceptions
Portforwarded ports 1433, 443, 5671-5672, and 9350-9354
Googled the hell out of it

What now?

Edit: I am using SQL Server 2017

Solution

I was using SQL Server 2017 - Express Edition, which does not have the SQL Server Agent available. This was rectified by switching to Developer Edition, which was suitable for my purposes.