"Simcom A7670G GSM Module: Failing to Send Large Data Payload via AT Commands from Raspberry Pi"

Question

I'm working on a project using a Raspberry Pi and a Simcom A7670G GSM module to send data to a server via AT commands. I've successfully sent smaller data payloads using the provided code. However, when attempting to send larger payloads, I encounter issues.

Using the following code:

(Initialization code)

procedure TSADSLA.GSMInitClick(Sender: TObject);
begin
   GSMSendCommand('AT', 'OK', true);
   GSMSendCommand('AT+CGDCONT=1,"IP","my_apn"', 'OK', true);
   GSMSendCommand('AT+CGATT=1', 'OK', true);
   GSMSendCommand('AT+CGACT=1,1', 'OK', true);
   GSMSendCommand('AT+CGPADDR=1', 'OK', true);
   GSMSendCommand('AT+HTTPINIT', 'OK', true);
   GSMSendCommand('AT+HTTPPARA="URL","my_url"', 'OK', true);
end;

(Data sending code)

procedure TSADSLA.GSMSendString(Data : string);
var
index1, startPos: Integer;
readLength: string;
begin
  GSMSendCommand('AT+HTTPDATA=' + IntToStr(Length(Data)) + ',15000', 'DOWNLOAD', true);
  GSMSendCommand(Data , 'OK', true);
  GSMSendCommand('AT+HTTPACTION=1', '+HTTPACTION:', false);
  index1:= Pos(',',GSMFeedbackString) +1;
  startPos := PosEx(',',GSMFeedbackString, index1+1);
  readLength := Copy(GSMFeedbackString,startPos+1,Length(GSMFeedbackString)-startPos + 1);
  GSMFeedbackString := '';
  GSMSendCommand('AT+HTTPREAD=' + readLength, 'OK', true);
end;

// ... (AT command handling code)

procedure TSADSLA.GSMSendCommand(command, response: string; clear : Boolean);
var
  timeout, counter : Integer;
begin
  timeout := 15000;
  counter:= 0;
  GSMSerial.WriteData(command + #13 + #10);
  while (counter < timeout) and (Pos(response,GSMFeedbackString) <= 0) do
  begin
    Sleep(1);
    Inc(counter);
    Application.ProcessMessages;
  end;

  if clear then GSMFeedbackString := '';

end;

I can successfully send data payloads of 50 lines (approximately 3000 characters). If I send more then that, after sending 'AT+HTTPACTION=1' command, I receive the response: "HTTPACTION:1,706,0" and I don't see the data on the server. When I connect the module to my PC using Windows and a terminal, I can successfully send larger payloads, such as 1000 lines. This is an example of 3 lines of the string I am sending(each line ending in a timestamp): "Logs/0/05-11-2023 18:26:18.csv D,BUK,BOT,133.92,+0.20,161.49,-0.03,157.16,+0.26,36,18:26:18,D,BUK,BOT,133.92,+0.20,161.49,-0.03,157.16,+0.26,36,18:26:18,D,BUK,BOT,133.92,+0.20,161.49,-0.03,157.16,+0.26,36,18:26:18,"

I had an older version of the string where the lines were separated by new lines and I could send even less characters, all I removed was the "+#13 + #10" at the end of each line and I suddenly could send 500 lines. 50 lines is what I have after adding "D,BUK,BOT," the timestamp and removing some numbers.

Baud rate is 115200.