DIAGNOSIS: The three beeps mean it doesn't detect the inner pot, or it thinks the pot is empty. The slow cook function requires the pot to be in place and has a minimum content requirement to work properly.
FIX: First, make sure you're using the correct, supplied inner pot (the big stainless steel one). The glass lid or air fry basket won't trigger the sensor. Place the pot firmly into the cooker, making sure it's sitting flat on the bottom heating element. Second, you need enough food/liquid in the pot. For slow cooking, it should be at least a quarter to a third full.
IF THAT DIDN'T WORK: Clean the bottom of the inner pot and the heating element area inside the main unit. A layer of grease or residue can interfere with the sensor's ability to detect the pot.
HEADS UP: The slow cook function on this multicooker runs at a higher wattage than a traditional, plug-in slow cooker. Things may cook faster, so check your recipes a bit earlier.