Need help calling function from C dll in vb.net

I am trying to use a function from ssdeep (http://ssdeep.sourceforge.net/) in my own program. The function name is fuzzy_hash_filename . The code I tried is below, however it always returns 1, meaning it failed. I'm not exactly sure what I'm doing wrong, any help would be appreciated :)

Private Declare Function fuzzy_hash_filename Lib "fuzzy.dll" Alias "fuzzy_hash_filename" (ByRef filename As String, ByRef result As String) As Integer
 
Dim str As String
Dim int as Integer
int = fuzzy_hash_filename("C:\test.txt", str)

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