I always start by giving my crockpot insert a light spray of nonstick cooking spray so nothing sticks and cleanup is easy later. Then I add my meatballs directly into the pot, spreading them out in an even layer. If you're using frozen meatballs, there's no need to thaw them first they'll cook through as the sauce heats up.
In a separate mixing bowl, I whisk the grape jelly, chili sauce, soy sauce, and chili flakes until everything is smooth and well combined. This only takes a minute or two, but it's worth doing in a separate bowl so the sauce coats every meatball evenly instead of pooling unevenly at the bottom of the crockpot.
Once my sauce is ready, I pour it directly over the meatballs in the slow cooker. Using a wooden spoon, I gently stir everything together so each meatball gets a good coating. Be gentle here stirring too roughly can break apart softer, homemade meatballs before they've had a chance to firm up.
I cover the crockpot and set it to high for about 3 to 4 hours, or low for around 6 hours if I'm prepping earlier in the day. Around the halfway mark, I give everything one more gentle stir so the sauce redistributes and nothing sticks to the bottom.
Once the meatballs are cooked through and the sauce has thickened slightly, I switch my slow cooker to the "warm" setting so it stays at serving temperature throughout the party. Right before guests arrive, I sprinkle on fresh chopped parsley for a pop of color that makes the dish look far more polished than the effort it took.
I like keeping the meatballs right in the slow cooker for serving since it keeps them warm for hours. I set out cocktail toothpicks nearby, or for a fun Halloween twist, I poke an apple or orange with festive toothpicks so guests can grab their own without digging through the sauce.