Connect Arduino to TCP and do HTTP Post

Question

I'm doing a project consisting of capturing temperature values ​​and sending them to an API. The main problem I'm having is Arduino Uno send AT commands to Esp8266 to get it connected. Here's my code:

void loop(){
  reset();
  while(connection == false)
    connectWifi();
  connection = false;
  httppost();
}

void connectWifi(){
  String cmd = "AT+CWJAP=\"" + ssid + "\",\"" + pass + "\"";
  delay(300);
  esp.println(cmd);
  if(esp.find("OK")){
    Serial.println("Wifi Connected");
    connection = true;
  }else{
    Serial.println("Wifi not Connected");
    connection = false;
  }
}

void httppost(){
  String postRequest =
        "POST " + uri + " HTTP/1.1\r\n" +
        "Host: " + server + ":" + port + "\r\n" +
        "Accept: *" + "/" + "*\r\n" +
        "Content-Length: " + data.length() + "\r\n" +
        "Content-Type: application/x-www-form-urlencoded\r\n" +
        "\r\n" +
        data;
  String tcpStart = "AT+CIPSTART=\"TCP\",\"" + ip + "\"," + port;
  String sendCmd = "AT+CIPSEND=" + postRequest.length();
  esp.println(tcpStart); //start TCP connection
  delay(300);
  if(esp.find("OK")){
    Serial.println("TCP connection OK");
    esp.println(sendCmd); //send the data over TCP connection
    delay(300);
    if(esp.find(">")){
      Serial.println("Sending packet");
      esp.println(postRequest);
      delay(300);
      if(esp.find("SEND OK")){
        Serial.println("Packet sent");
        while(esp.available()){ //number of bytes/char available for reading
          char tmpResp = esp.read(); //read one char at the time
          Serial.print(tmpResp);
          if (tmpResp == '\0') continue; //terminate the while when end of the data
        }
        esp.println("AT+CIPCLOSE"); //close TCP connection
      }else{
        Serial.println("An error occured while sending packet");
      }
    }else{
        Serial.println("ESP8266 is not listening for incoming data");
    }
  }else{
    Serial.println("Cannot initiate TCP connection");
  }
}

Here's an output example I get:

So the problem seems to be the execution of the AT command: AT+CIPSTART. I've done several searches but I can't figure out why it isn't working.