diff --git a/lib/core/SessionBuilder.js b/lib/core/SessionBuilder.js
index 0f2103a2..e6ec0890 100644
--- a/lib/core/SessionBuilder.js
+++ b/lib/core/SessionBuilder.js
@@ -44,7 +44,7 @@ class SessionBuilder {
     const user_agent = new UserAgent({ deviceCategory: 'desktop' });
     
     const id = Utils.generateRandomString(11);
-    const timestamp = new Date().getTime();
+    const timestamp = Math.floor(Date.now() / 1000);
     
     const visitor_data = Proto.encodeVisitorData(id, timestamp);
     
diff --git a/lib/proto/index.js b/lib/proto/index.js
index 9fe87e82..cf96d8b8 100644
--- a/lib/proto/index.js
+++ b/lib/proto/index.js
@@ -13,7 +13,7 @@ class Proto {
    */
   static encodeVisitorData(id, timestamp) {
     const buf = messages.VisitorData.encode({ id, timestamp });
-    return encodeURIComponent(Buffer.from(buf).toString('base64'));
+    return encodeURIComponent(Buffer.from(buf).toString('base64').replace(/\//g, '_'));
   }
   
   /**