ESP32 send large file (http post) to server from LittleFS - https

Question

I'm trying to post a (large) json file that's stored in the SPIFFS (LittleFS- of an arduino.
I first of all, fetch the JSON from a local IP address, which can change or is dynamic. Then, that json file gets stored in the internal flash of my ESP32 and sent over to our servers.
The goal is to have an ESP32 act as a bridge for local addresses.
For example:
Locally, there is a server running, that server is never accessible from outside of a network, but it is from within. We place an ESP32 in that network, to be able to read out data from the internal device and pass them through to our servers, for further processing.
The current code I have is the following;
HTTPClient http;
if (LittleFS.exists("/downloadedFile.json")) {
LittleFS.remove("/downloadedFile.json");
}
File f = LittleFS.open("/downloadedFile.json", "w", true);
if (f) {
String url;
// Build the URL...
if (username != "" && password != "") {
url = "http://" + username + ":" + password + "#" + ip + ":" + String(port) + "/data/file.json";
} else {
url = "http://" + ip + ":" + String(port) + "/data/file.json";
}
http.begin(url);
int httpCode = http.GET();
if (httpCode > 0) {
if (httpCode == HTTP_CODE_OK) {
http.writeToStream(&f);
}
} else {
// failed.
}
f.close();
} else {
// Unable to open file
}
http.end();
if (LittleFS.exists("/downloadedFile.json")) {
File f = LittleFS.open("/downloadedFile.json", "r");
if (f) {
WiFiClienSecure client;
client.setInsecure(); // test
if (!client.connect("my.somain.com", 443)) {
// failed to connect. (never gets in here)
return;
}
client.println("POST /path/to/my/endpoint HTTP/1.1");
client.println("Host: my.somain.com");
client.println("Content-Type: application/json");
client.println("Connection: keep-alive");
client.println("Content-Length: " + String(f.size()));
client.println();
// Build the body
int len = 0;
int total = 0;
uint8_t buf[1025] = {};
size_t _len = 256;
do {
len = f.read(buf, _len);
client.write(buf, len);
total += len;
} while (len > 0);
client.println(); // end line
client.stop();
f.close();
}
}
Downloading the file always works, except for sometimes random crashing the whole system. But that's the least of my concerns.
Locally I got it working to download and re-upload the file. Struggle is when I try to achieve the same result on the server (which uses https)
Only difference is this;
Server
Local
WiFiClienSecure client;
WiFiClient client;
client.setInsecure();
client.connect("my.somain.com", 443)
client.connect("IP", 80)
The main problem is that it doesn't work on the server and that it works really unstable. the file size (when I do f.size()) is 310831.
Any help and thoughts on getting this stable is appriciated!