diff --git a/lib/datahappy/datahappy.go b/lib/datahappy/datahappy.go
index 7e373cd..6efe9b9 100644
--- a/lib/datahappy/datahappy.go
+++ b/lib/datahappy/datahappy.go
@@ -16,16 +16,18 @@ var library = &Library{
 type Client struct {
 	client *jsonclient.Client
 
+	ProjectID string
 	AuthToken string
 }
 
-func NewClient(baseURL, authToken string) *Client {
+func NewClient(baseURL, projectID, authToken string) *Client {
 	return &Client{
 		client: jsonclient.NewClient(
 			baseURL,
 			httpclient.NewClient(5*time.Second, nil),
 		),
 
+		ProjectID: projectID,
 		AuthToken: authToken,
 	}
 }
diff --git a/lib/datahappy/track.go b/lib/datahappy/track.go
index 6bdef98..8059078 100644
--- a/lib/datahappy/track.go
+++ b/lib/datahappy/track.go
@@ -17,6 +17,7 @@ const (
 )
 
 type TrackRequest struct {
+	ProjectID    string         `json:"projectId"`
 	Type         RequestType    `json:"type"`
 	AnonymousID  string         `json:"anonymousId,omitempty"`
 	UserID       string         `json:"userId,omitempty"`
@@ -34,6 +35,10 @@ func (c *Client) Track(ctx context.Context, req *TrackRequest) error {
 	// ensure no mutation of the original request
 	req = ptr.ShallowCopy(req)
 
+	if req.ProjectID == "" {
+		req.ProjectID = c.ProjectID
+	}
+
 	if req.Type == "" {
 		req.Type = RequestTypeTrack
 	}