In no case, we do not store your customers' data.
Our Salesforce instance is hosted on UM5 server which is based in EMEA. We only store data on our users - the minimum data we need for the product to work, and user preferences (like field customization and account settings). You can find more information about it on our Data Processing Agreement and Security documentation.
For example, we store data such as: WhatsApp phone, SF User's first name, SF User's last name, SF User's username, SF User's email, SF User's profile, SF User's job title, SF User's country, SF User's state, SF User's city, browser locale, language, Tuvis user creation date, last Tuvis activity date, Tuvis user field layout settings, etc.