Color ID Help

high

low

I am baking a high poly model down to a low poly one, and I have things setup in such a manner where the high-poly wraps here will be directly baked on to the low poly handle,, which is completely flat.

I would like to mention that in this model, the ENTIRE handle is joined as one, from the top of the handle to the bottom (where you see that little circular jutt). The high poly is setup the same way, with the exception of the wraps of course. I have already UV unwrapped the low-poly.

I am texturing in substance painter, so I need to set a color ID to those high poly wraps so I can properly texture them once I move to substance painter. Problem is, I have no clue HOW to do that. I looked at tutorials (which are all insanely old), and when I follow the instructions, I get stuck.

Specifically, I just get a missing texture/stencil error.

My steps:

Edit mode on the high poly mesh, select only the wrap faces, enter texture paint, enter mask mode, and get the error.

I even decided to make a very simple, separate model and follow the steps. got specifically a missing stencil error, and nothing else. Im not that good with the program yet I have no clue what this means.

Im assuming theres something incorrect with my material? Or maybe my UV? I have no clue. I've been stumped for around half an hour, so I just logged off and decided to make this post.