The stew shouldn’t be too runny. I like to thicken it with either normal flour or gluten-free gram flour. Gram flour works great for thickening any meal containing pulses.    Pre-mix the flour in a mug with a small quantity of water before stirring it into the stew. If you try to add the flour directly to the stew it will most likely clump.   I prefer to mix flour with fairly warm (but not boiling) water. It feels like this way it’s easier to make a smooth flour mix with a minimal number of lumps.   My last recommendation is to turn the heat down or set the pot aside to stop it from boiling before adding the flour mix in. Stir properly when adding the flour to prevent lumps that can happen when thickening agent touches the hot liquid. After that increase the temperature again. Boil the stew for at least 3 more minutes and stir occasionally.