diff --git a/core/archipelago/src/mesh/protocol.rs b/core/archipelago/src/mesh/protocol.rs
index 9df5cc28..ccb23835 100644
--- a/core/archipelago/src/mesh/protocol.rs
+++ b/core/archipelago/src/mesh/protocol.rs
@@ -222,6 +222,10 @@ pub fn build_send_text(dest_pubkey_prefix: &[u8; 6], msg: &[u8]) -> Result<Vec<u
 }
 
 /// CMD_SEND_CHANNEL_TXT_MSG (0x03): Broadcast a text message on a channel.
+/// Frame layout per meshcore companion protocol:
+///   `[0x03][txt_type=0][channel][timestamp_le32][text…]`
+/// The txt_type and timestamp fields are mandatory — without them the
+/// firmware rejects the command with ERR_UNSUPPORTED.
 pub fn build_send_channel_text(channel: u8, msg: &[u8]) -> Result<Vec<u8>> {
     if msg.len() > MAX_MESSAGE_LEN {
         anyhow::bail!(
@@ -230,7 +234,12 @@ pub fn build_send_channel_text(channel: u8, msg: &[u8]) -> Result<Vec<u8>> {
             MAX_MESSAGE_LEN
         );
     }
-    let mut data = vec![CMD_SEND_CHANNEL_TXT_MSG, channel];
+    let timestamp = std::time::SystemTime::now()
+        .duration_since(std::time::UNIX_EPOCH)
+        .map(|d| d.as_secs() as u32)
+        .unwrap_or(0);
+    let mut data = vec![CMD_SEND_CHANNEL_TXT_MSG, 0x00, channel];
+    data.extend_from_slice(&timestamp.to_le_bytes());
     data.extend_from_slice(msg);
     Ok(encode_frame(&data))
 }
@@ -697,10 +706,13 @@ mod tests {
 
     #[test]
     fn test_build_send_channel_text() -> Result<()> {
-        let frame = build_send_channel_text(0, b"test")?;
+        let frame = build_send_channel_text(2, b"test")?;
+        // Frame: [marker][len_lo][len_hi][cmd][txt_type][channel][ts(4)][text]
         assert_eq!(frame[3], CMD_SEND_CHANNEL_TXT_MSG);
-        assert_eq!(frame[4], 0); // channel 0
-        assert_eq!(&frame[5..], b"test");
+        assert_eq!(frame[4], 0); // txt_type
+        assert_eq!(frame[5], 2); // channel idx
+        // frame[6..10] = timestamp, non-deterministic
+        assert_eq!(&frame[10..], b"test");
         Ok(())
     }