Invalid Grant - Malformed Auth Code

[reubenhhhh]

Hiya - Trying to migrate over from the Homebridge Nest Cam plugin since I just added a new camera and had to go through the Google Home flow rather than Nest app. Unfortunately I keep getting the following error...
"error": "invalid_grant",
"error_description": "Malformed auth code."

Any insight on what I'm doing wrong would be appreciated.

Many thanks in advance.