The "polylines" parameter must be a stringified JsonArray object containing the polylines vertices and attributes.

These vertices must be JsonArray objects too, and must contain the latitude first and the longitude second in the WGS84 projection.
Therefore, the latitude value must be between -85 and +85 and the longitude one must be between -180 and +180.
You need at least 2 vertices to make a polyline.
The attributes must be represented by a JsonObject containing attribute name/attribute value pairs.
Date Type Attribute if add a geometry with a date type attribute. Date value format : dd-MM-yyyy (example 12-02-2016)
For example :

var polylinesAsJsonArray = [{"vertices":[[43.5,3.8],[44.2,3.4],[43.9,4.1]], "attributes":{"Name":"Viktor Blom","Phone":0033123456789,"Age":25}},
{"vertices":[[43.7,3.4],[44.2,3.7],[42.9,4.5]], "attributes":{"Name":"Doug Polk","Phone":0033123789456,"Age":26}},
{"vertices":[[42.1,3.2],[45.2,3.4],[43.6,4.1]], "attributes":{"Name":"Alexandre Luneau","Phone":0033456789123,"Age":28}}];
var polylines = JSON.stringify(polylinesAsJsonArray);

If successful, this method adds the polylines to the mapdata defined by the "mapdatName" parameter and returns a 200 HTTP response containing the newly added polylines ids.