A blender often needs liquid to move, but a spread needs enough body to stay on bread. The two requirements are easier to balance when you add liquid gradually.
Start with soft cooked beans, some oil or another suitable creamy ingredient, and a small amount of water or cooking liquid. Blend, stop, and scrape down with the machine safely switched off. Add another spoonful only when needed.
If the motor is struggling, follow the appliance's instructions rather than forcing it through a stiff mixture. A food processor or potato masher may be more suitable for a small batch, especially if you enjoy some texture.
Season once the consistency is close. Lemon juice also adds liquid, so account for it before thinning everything with water. A spread that seems loose while warm may firm somewhat when chilled, depending on its ingredients.