I've found the solution: a middleware inside my main.py based on this class. The full code of my main.py is now the following.

from flask import Flask, render_template, request
from groq import Groq

# App configuration
model_id = "qwen/qwen3-32b"
groq_api_key = "<--my API key :)-->"
PREFIX = "/qwen"

# PrefixMiddleware auxiliary class
class PrefixMiddleware:
    def __init__(self, app, prefix):
        self.app = app
        self.prefix = prefix

    def __call__(self, environ, start_response):
        path = environ.get('PATH_INFO', '')
        if path.startswith(self.prefix):
            environ['SCRIPT_NAME'] = self.prefix
            environ['PATH_INFO'] = path[len(self.prefix):] or '/'
        return self.app(environ, start_response)

# App definition
app = Flask(__name__)
app.wsgi_app = PrefixMiddleware(app.wsgi_app, PREFIX)
client = Groq(api_key=groq_api_key)

# Flask routes
@app.route('/')
    def index():
    return render_template('index.html')

@app.route('/answer', methods=['POST'])
    def answer():
    input_text = request.form.get('input_text')
    if not input_text:
        return "Please provide input text.", 400
    try:
        completion = client.chat.completions.create(
            model=model_id,
            messages=[
                {"role": "system", "content": "User chatbot"},
                {"role": "user", "content": input_text}
            ],
            temperature=1,
            max_tokens=1024,
            top_p=1,
            stream=True,
            stop=None,
        )
        result = ""
        for chunk in completion:
            result += chunk.choices[0].delta.content or ""
    except Exception as e:
        return f"An error occurred: {e}", 500

    return render_template('index.html', input_text=input_text, result=result)

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

In the Kubernetes Ingress, I also removed the annotation. The other files are the same.