In this video

After ensuring the patched area is completely smooth and free of dust, apply a coat of primer, sealer, and undercoat. The video suggests using "Dulux 1 Step Prep Primer, Sealer & Undercoat." Apply the primer evenly over the entire patched area and extend it slightly onto the surrounding wall. This step is essential to seal the porous plasterboard and ensure that the topcoat of paint adheres properly and has a uniform finish, preventing flash marks or differences in sheen. Allow the primer to dry completely according to the product's instructions.