You mentioned in a comment you're trying to make solid chocolate, like chocolate bars?
Sugar simply doesn't dissolve in fats like cocoa butter, and you have no water or other liquid... and if you did you'd get a softer chocolate confection, more like fudge, rather than hard chocolate like bars. To make solid chocolate at home, the smooth kind, you will need some kind of conching or grinding equipment - something to grind the chocolate and sugar together to make it smooth and so that it stays well mixed together.
I believe that sugar will also settle, so just mixing powdered sugar into a liquid cocoa-powder-and-butter mixture isn't found in homemade chocolate recipes - it won't stay suspended and evenly spread through your chocolate mixture. Larger sugar crystals might actually stay suspended better, not settle as much, that is why mexican-style chocolate (with crunchy sugar crystals) is a thing. I've seen some recipes that use honey or syrup but the resulting chocolate will tend to be softer. One recipe used sugar at one-string consistency (a candymaking syrup), that might be your best bet for something like chocolate bars, if you want to go that far.
You can much more easily make chocolate confections like fudge, that have added water for the sugar to dissolve into, that is what most people end up doing and they can be very good. That's what mfg was doing, from their answer. And some of them might end up fairly close to solid chocolate, if that is what you're looking for, if you're using minimum sweetners and going for a very dark, bittersweet chocolate candy.
If you're interested in making chocolate properly with conching, there are dedicated grinders and also some Indian-style wet grinders can work, if you check the settings. It sounds like a lot of fun, if also a lot of work.