Hello,
Simple precision, perhaps useless: you have to double click on the correct element in the extension for the filling to be done.
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I propose the following small experience.
1. In Enpass, select the item that is causing you a problem.
2. In your browser, go to the page that asks for your username and password.
3. In Enpass, copy your username using the two small squares to the right of the line.
Paste your ID on the site where you want to connect.
4. Do the same thing with the password.
Results?
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User guide: https://www.enpass.io/user-guide
FAQ: https://www.enpass.io/support/