master is able to send negative value

Code/ESP32_communication/test_more_variables/ESP32_master/ESP32_master.ino

+//-----------------------------------------------------------
+//ESP-NOW: Transmitter
+//Ref: Random Nerd Tutorials https://randomnerdtutorials.com
+//-----------------------------------------------------------
+#include <esp_now.h>
+#include <WiFi.h>
+//-------------------------------------------------------------------------------------
+uint8_t RxMACaddress[] = {0xC4, 0xDD, 0x57, 0x9E, 0x91, 0x74};
+String strdata = "";
+String valdata = "";
+int count = 0;
+//-------------------------------------------------------------------------------------
+typedef struct TxStruct
+{
+  String StrD;
+  double ValD;
+}TxStruct;
+TxStruct sentData;
+//-------------------------------------------------------------------------------------
+void OnDataSent(const uint8_t *mac_addr, esp_now_send_status_t status) //callback function
+{
+  Serial.print("\r\nLast Packet Send Status:\t");
+  Serial.println(status == ESP_NOW_SEND_SUCCESS ? "Delivery Success" : "Delivery Fail");
+}
+//======================================================================================
+void setup()
+{
+  Serial.begin(9600);
+  WiFi.mode(WIFI_STA);
+  //------------------------------------------------------------------------------------
+  if(esp_now_init() != ESP_OK)
+  {
+    Serial.println("Error initializing ESP-NOW");
+    return;
+  }
+  //-------------------------------------------------------------------------------------
+  esp_now_register_send_cb(OnDataSent);
+  //-------------------------------------------------------------------------------------
+  esp_now_peer_info_t peerInfo;
+  memcpy(peerInfo.peer_addr, RxMACaddress, 6);
+  peerInfo.channel = 0;  
+  peerInfo.encrypt = false;
+  //-------------------------------------------------------------------------------------
+  if(esp_now_add_peer(&peerInfo) != ESP_OK)
+  {
+    Serial.println("Failed to add peer");
+    return;
+  }
+}
+//======================================================================================
+void loop()
+{ 
+  while (Serial.available()>0){
+    int inChar = Serial.read();
+    /*
+    sentData.potVal = inChar - '0';
+    delay(10);
+    esp_now_send(RxMACaddress, (uint8_t *) &sentData, sizeof(sentData));
+    delay(500);
+    */
+   strdata += char(inChar);
+   delay(10);
+   count +=1;
+   if (count == 3){
+    sentData.StrD = strdata;
+    Serial.println(sentData.StrD);
+   }
+  if (isDigit(inChar) || inChar == '.' || inChar == '-'){
+    valdata += char(inChar);
+  }
+  
+  if (inChar == '\n'){
+   sentData.ValD = valdata.toDouble();
+   Serial.println(sentData.ValD);
+  esp_err_t result = esp_now_send(RxMACaddress, (uint8_t *) &sentData, sizeof(sentData));
+  // esp_now_send(RxMACaddress, (uint8_t *) &sentData, sizeof(sentData));
+  //-------------------------------------------------------------------------------------
+  if (result == ESP_OK) Serial.println("Sent with success");
+  else Serial.println("Error sending the data");
+  //-------------------------------------------------------------------------------------
+  delay(500);
+  strdata = "";
+  valdata = "";
+  count = 0;
+  }
+  
+  }
+
+  //-------------------------------------------------------------------------------------
+  
+}