The function string::LastIndexOf has a copy-paste mistake in the docs in the line that Prints the result.
Also, the function seems to be accidentally not linked on the c++ side. I would assume it is a quick and easy fix.
Here is the fixed docs:
/**
\brief Finds last 'sample' in 'str'. Returns -1 when not found
\param sample \p string Finding string
\return \p int - Returns position where \p sample starts, or -1 when \p sample not found
@code
string str = "Hello World";
Print( str.LastIndexOf( "l" ) );
>> 9
@endcode
*/
proto native int LastIndexOf(string sample);