I was trying to create a chatbot using dialogflow, VS Code, python, flask, an API and ngrok. I tried hard to find the solution of this problem but still unsuccessful. With heavy heart, I decided to share it with my stack overflow community.

Here is the full flask backend code:

from flask import Flask,request,jsonify
import requests

app = Flask(__name__)

@app.route('/',methods=['POST'])
def index():
    data = request.get_json()
    source_currency = data['queryResult']['parameters']['unit-currency']['currency']
    amount = data['queryResult']['parameters']['unit-currency']['amount']
    target_currency = data['queryResult']['parameters']['currency-name']


    cf = fetch_conversion_factor(source_currency,target_currency)
    final_amount = amount * cf
    final_amount = round(final_amount,2)

    response = {
        'fulfillmentText':"{} {} is {} {}".format(amount,source_currency,final_amount,target_currency)
    }
    return jsonify(response)

def fetch_conversion_factor(source,target):
    url = "https://prepaid.currconv.com/api/v7/convert?q={}_{}&compact=ultra&apiKey=cf50a6e1e1a9bf32f3b9".format(source,target)

    response = requests.get(url)
    response =  response.json()

    return response['{}_{}'.format(source,target)]

if __name__ == "__main__":
    app.run(debug=True)

and here is raw API response(on dialogflow):

{
  "responseId": "adb7509a-add5-4674-b4ad-6bff5e541b52-0e7b65aa",
  "queryResult": {
    "queryText": "convert 500 USD to INR",
    "parameters": {
      "unit-currency": [
        {
          "currency": "USD",
          "amount": 500
        }
      ],
      "currency-name": [
        "INR"
      ]
    },
    "allRequiredParamsPresent": true,
    "fulfillmentText": "Error! Please try again later.",
    "fulfillmentMessages": [
      {
        "text": {
          "text": [
            "Error! Please try again later."
          ]
        }
      }
    ],
    "intent": {
      "name": "projects/moneybot-tv9q/agent/intents/ef5701ea-afb0-4700-a28b-b5c78495b8d9",
      "displayName": "currency-convertor"
    },
    "intentDetectionConfidence": 1,
    "diagnosticInfo": {
      "webhook_latency_ms": 1052
    },
    "languageCode": "en",
    "sentimentAnalysisResult": {
      "queryTextSentiment": {}
    }
  },
  "webhookStatus": {
    "code": 14,
    "message": "Webhook call failed. Error: UNAVAILABLE, State: URL_UNREACHABLE, Reason: UNREACHABLE_5xx, HTTP status code: 500."
  }
}

Please help me to solve this problem as I am very depressed. I am trying to solve this problem from last 2 days. I searched on all platform but still no solution.