The following snippet creates an API to recieve 2 numbers and return their sum.

flask_api1.py

from flask import Flask, request

app = Flask(__name__)


@app.route('/', methods=['GET'])
def add():
    num1 = request.args.get('num1')
    num2 = request.args.get('num2')
    return num1 + num2


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