Clone Tool is greyed out in Substance Painter. I'm stuck!

Hello! 

I'm trying to use the clone tool with all the layers set as Passthrough so I can create a tilebale texture. Unfortunately the clone tool is greyed out. I'm not sure what I'm doing wrong - thanks!

-Sylvia M

NB: I'm using Version 9.0.0 build 2585, Apple Mac M1 Ultra, Sonoma 14.1