Mattes not working on the color tab

I'm using Davinci Resolve Studio 17.3.2. For some reason, I can't use MATTES in the color page. If I try to connect the "Ext Matte" to the "Serial Node". The Serial Node turns gray. Then, I connect the "Ext Matte" node to the "Alpha Output" node and the color page viewer turns black. Or if I connect the "Serial Node" to the "Alpha Output" the color viewer turns black. Am I doing this incorrectly or is there a bug present? (Apologize if there is a topic on this already or if this is the incorrect place for this message)

[Peter Chamberlain]

Try inverting the matte in the matte palette

Can you give me instruction on how to do that?

Where is the matte platette? (sorry if responded twice)