It sounds like the Data Saving Mode in Opera Mini is interfering with the login process on the Hodfords website. This mode often compresses web content to save data, which can sometimes disrupt interactive elements like login forms.

Here are a few steps you can try to resolve this issue:

Disable Data Saving Mode: Temporarily turn off Data Saving Mode and try logging in again. This can help determine if the mode is the root cause.
Clear Cache and Cookies: Sometimes, cached data can cause problems with website functionality. Clear your browser's cache and cookies, then attempt to log in again.
Check for Updates: Ensure your Opera Mini browser is up to date. Sometimes bugs are fixed in newer versions.
Use a Different Browser: If the issue persists, try logging in using another browser on your device, like Chrome or Samsung Internet, to see if the problem is specific to Opera Mini.

Regarding technical adjustments, it's challenging to modify headers or JSON formats directly from a mobile browser. However, if you have access to the backend of the website, you might check if there are any specific configurations for handling requests from Opera Mini.