: When making requests, ensure that your client (whether it's a web application, mobile app, or a backend service) is set to use UTF-8 encoding. This ensures that any text data, including email addresses that might contain non-ASCII characters, are properly encoded.
Log into the Ubisoft Account Management website via a browser (not the launcher). Change your email address to the most boring, ASCII-only address possible: FirstnameLastname@proton.me or GamerTag@gmail.com . Avoid dots, plus signs, or special characters. uplay user get email utf 8