You need to acquire both strategic resources. This will allow you to build the refinery, which then slowly generate ketracel white. You can see whatever you generate white in the strategic resources list.

White is an accumlated resource - every month you will generate 5 units, per refinery. This does not appear in the strategic resource list but an invisible value kept in the background. If you hover over the jem'hadar, you will see that the amount of white you need (originally 150) will slowly decline in time, until you accumlated enough, and then you can build a jem'hadar.

Ah thank you for the quick response. I had built the refinery on the tile with the two necessary ingredients, which voids their harvesting. I tried building it on a different tile, and now I'm generating Ketracel White as intended.