It looks like your Package variable is invalid, since it’s the package that precedes the ‘.’ in the asset path. How have you obtained/created the package?
I created the package too but I don’t think that this should be the problem since the materials are created properly in their package but I cannot save them
FString overloads the / operator to make it easier to concatenate paths without worrying about separators.
GetLongPackagePath will take a full package path and cut off the name from the end to give you the location of the package.
Ufff materials are not saved yet, they seems to be (the asterisks are gone when clicking on save) but reopening the project they are not more there. If I edit it like moving a node or whatever and click on save they are saved properly!