Nativescript Angular IOS APP - Unable to upload photos to API/Server in slow network

Question

Our Nativescript Angular IOS App is running on Nativescript version 8.4.7 and angular 15.

When uploading more than 2 photos to server/ Microsoft api in the slow network (LTE 1 or 2 bars). The photos are not uploading and returning below exception. Looks like the request is not even reaching the server.

error
  {
    "headers": {
      "normalizedNames": {},
      "lazyUpdate": null,
      "headers": {}
    },
    "status": 0,
    "statusText": "Unknown Error",
    "url": "https://abc",
    "ok": false,
    "name": "HttpErrorResponse",
    "message": "Http failure response for "https://abc": 0 Unknown Error",
    "error": {}
  }

can anyone help me on how to fix this issue or is there any setting on the ios/nativescript/angular side which will prevent this to happen?

When connected to a strong network LTE 3 or more bars ,5g or WIFI , I am able to upload more than 50 photos at once without any issues.

I am doing angular HTTPClient Post for each photo and sending the object in the post body as json.