Hi @LetsCode,
I am pretty sure that there is page with the error codes written down, but I can’t remember where it is - maybe @amandus knows…
In general though you should not get error codes starting with 4 from the directions end point as those error codes are for the POI service. If you mean 2003 and 2004, then those signify that there is an incorrect parameter value in the request (e.g. you have used too few coordinates or told it to avoid a feature type that is not supported), and 2004 means that the request exceeds some limit relating to the route (e.g. route is too long for the specified profile/restrictions combination).