云服务器微信无法发送图片

from flask import Flask, request, redirect, url_for
import os

app = Flask(__name__)
UPLOAD_FOLDER = '/path/to/upload/folder'
ALLOWED_EXTENSIONS = {'png', 'jpg', 'jpeg', 'gif'}

app.config['UPLOAD_FOLDER'] = UPLOAD_FOLDER

def allowed_file(filename):
    return '.' in filename and filename.rsplit('.', 1)[1].lower() in ALLOWED_EXTENSIONS

@app.route('/upload', methods=['POST'])
def upload_file():
    if 'file' not in request.files:
        return 'No file part'
    file = request.files['file']
    if file.filename == '':
        return 'No selected file'
    if file and allowed_file(file.filename):
        filename = secure_filename(file.filename)
        file.save(os.path.join(app.config['UPLOAD_FOLDER'], filename))
        return 'File successfully uploaded'
    else:
        return 'Invalid file type'

if __name__ == '__main__':
    app.run(host='0.0.0.0', port=5000)