It is not growing directly on the bare liner. I'm not sure if that would even be possible but wjat I did was use a texturing coat to make the liner accept moss.There is a product made by quikrete for patching concrete that is acrylic based and used that to make a texture on the flat part of the liner as it goes over the edge and then you just have to plant the moss from the nursery onto the textured surface and it will grow almost to the waters edge and also grows good on the rocks especially of my smaller pond, The large turtle pond has not been planted yet because I have never textured the liner or did much of anything to that one.
After the acrylic based product (can you share the name?) how did you plant the moss?