The libraries you need are listed in the “Learn” section under installing and using the Arduino IDE. Some of those won’t be needed in your particular case. Those that are needed are listed in the documentation here: 3-phase 3&4-wire PLL - V1.7: Update to 3-Phase PLL sketch - #21 by Robert.Wall
And there are more notes in the sketch source code itself. One that might throw some light on your interfacer problem is the comment in line 60: “For serial input, emonHub requires “datacode = 0” in place of “datacodes = …” as above.” Which is because, when you send the serial data - and as you can see by looking at the sketch - it arrives as plain text that does not need decoding, hence the zero or no datacode.
You should read the documentation, because it contains (we hope) useful information for you.