I have not used a tumbler type but may need some moisture. It takes moisture to heat up and in your hot sun may have dried out your mixture.
As for the kibble it may have things in the mix such as oil/animal fat that would slow the process but should still work , maybe just slower.

I've never used a tumbler, either, but I've heard that they are slower than composting on the ground. In that case, organisms from the soil, and well as insects, enter the mix to help the process. Maybe try adding some soil?

For the process to work at it's best, you need the right C:N ratio, the proper moisture level, adequate oxygen... You shouldn't need compost starter.

Karen

Thank you, Cinda and Kara. I think I need to dump it all on the ground...couldn't hurt!

I give my tumbler a good hose watering once a week if possible, especially when our long dry period comes about, or lately when we had rains, I open the lid, allow it to get wet, close the lid, tumble it, leave it alone. It works for me.

I did not have pets before, so no pet scraps there..and my current pet is a cat which eats up all that is served to him. So all I put there in my tumbler are leaves, catkins, some old fruits, kitchen scraps.