https://www.bbc.com/news/technology-65139406
The Italian data-protection authority said there were privacy concerns relating to the model, which was created by US start-up OpenAI and is backed by Microsoft.
The regulator said it would ban and investigate OpenAI "with immediate effect".
GDPR governs the way in which we can use, process and store personal data.
The watchdog said on 20 March that the app had experienced a data breach involving user conversations and payment information.
It said there was no legal basis to justify "the mass collection and storage of personal data for the purpose of 'training' the algorithms underlying the operation of the platform".