When S. Fomin and A. Zelevinsky invented cluster algebras about 20 years ago,  one of their hopes was that the cluster monomials would be part of a ‘canonical’  basis. This naturally led them to the conjecture that cluster monomials should be linearly independent. This conjecture has been proved recently by Gross-Hacking-Keel-Kontsevich using scattering diagrams.   In this talk,  our aim is to use the additive categorification of the skew-symmetrizable cluster algebras of finite type to check that cluster monomials are linearly independent in such cluster algebras. This is joint work with C. Fu and S. Geng.