Suddenly all my devices stopped uploading information to ThingSpeak

I have 4 devices composed by 1 Arduino Nano and 1 SIM808 GPRS Módule which sends information about a facility to ThingSpeak and alarm SMS when some variables meet a certain condition.

Currently the 4 devices continue sending SMS but suddenly stopped uploading information to ThingSpeak on May 9 of this year. They have been placed in different cities, with SIM cards from different providers, for 2 years. Could it be that the way information is uploaded to ThingSpeak has changed?

I tried ingesting a single point into my channel using the browser (based on what was indicated in the documentation) and It worked.

Because of that I think the problem is that the code I use to upload information to Thingspeak no longer works.

The function I created to upload information to thingspeak is below:

//Función en envía datos a la plataforma ThingSpeak
void msj_ThingSpeak(){
wdt_reset();    
mySerial.println("AT+CIPSTATUS"); //Consultar el estado actual de la conexión
delay(2000);  
mySerial.println("AT+CIPMUX=0"); //Comando configura el dispositivo para una conexión IP única o múltiple. 0 = única
delay(3000);
updateSerial();
wdt_reset();    
mySerial.println("AT+CSTT=\"igprs.claro.com.ar\",\"clarogprs\",\"clarogprs999\""); //Configura el APN, usuario y contraseña.
delay(1000);
updateSerial();
mySerial.println("AT+CIICR"); //Comando para realizar una conexión inalámbrica con GPRS o CSD
delay(3000);
updateSerial();
wdt_reset();     
mySerial.println("AT+CIFSR"); //Obtener nuestra IP local
delay(2000);
updateSerial();
mySerial.println("AT+CIPSPRT=0"); //Establece un indicador '>' al enviar datos
delay(3000);
updateSerial();
wdt_reset(); 
mySerial.println("AT+CIPSTART=\"TCP\",\"api.thingspeak.com\",\"80\""); //Indica tipo de conexión, url o dirección IP y puerto de la conexión
delay(6000);
updateSerial();
wdt_reset();     
mySerial.println("AT+CIPSEND"); //Envía datos a través de una conexión TCP o UDP
delay(4000);
updateSerial();
wdt_reset();     
String datos="GET https://api.thingspeak.com/update?api_key=xxxxxxxxxxxxxxxx&field4=0" + String(promedio); 
mySerial.println(datos); //Envía los datos al servidor remoto
delay(4000);
updateSerial();
wdt_reset();    
mySerial.println((char)26); //Envía el caracter "Enter"
delay(5000); //Ahora se espera una respuesta
mySerial.println();
updateSerial();
wdt_reset(); 
mySerial.println("AT+CIPSHUT"); //Cierra la conexión(Desactiva el contexto GPRS PDP)
delay(5000);
updateSerial();
wdt_reset(); 
Serial.flush();  //Limpiamos puertos serie
mySerial.flush();
} 

[Christopher Stapels]

There seem to be several user reporting a change in behavior, though I am aware of no updates on that date. Ill update if I find if anything changed.