diff --git a/src/modem.rs b/src/modem.rs
index 6c2390a..9bda57a 100644
--- a/src/modem.rs
+++ b/src/modem.rs
@@ -185,7 +185,7 @@ impl<UART: serial::Uart> Modem<UART> {
         self.read_response(cmd.contains, cmd.timeout)
     }
 
-    fn send_data(&mut self, payload: &str) -> Result<String> {
+    fn send_data(&mut self, buf: &[u8]) -> Result<String> {
         self.rx.clear();
         let _ = self.send_bytes("AT+CIPSEND".as_bytes(), '\r')?;
         let send_request: String = self.rx.reset(Duration::from_millis(3000))
@@ -196,7 +196,7 @@ impl<UART: serial::Uart> Modem<UART> {
             return Err(ModemError::SendDataError);
         }
 
-        self.send_bytes(payload.as_bytes(), 26 as char)?; // 26_u8 = Ctrl+z - to end sending data
+        self.send_bytes(buf, 26 as char)?; // 26_u8 = Ctrl+z - to end sending data
         let _ = self.read_response(Some("DATA ACCEPT".to_string()), Duration::from_millis(3000));
 
         self.rx.clear();
@@ -263,8 +263,8 @@ impl<UART: serial::Uart> Modem<UART> {
         Ok(())
     }
 
-    pub fn tcp_send(&mut self, payload: &str) -> Result<()> {
-        self.send_data(payload)?;
+    pub fn tcp_send(&mut self, buf: &[u8]) -> Result<()> {
+        self.send_data(buf)?;
         Ok(())
     }