The reason you are seeing this message is because you have selected the 'Automate my authentication and skip associated pop-ups' option in Quick Settings.
Lean Library browser extension is applying QUB Library proxy to all URLs you are trying to access.
To remove this setting, you can un-select this option.
The reason you are seeing this message is because Lean Library cannot detect a DOI on the webpage.
If there is no DOI or ISBN on the webpage Lean Library extension will not be able to extract the data and search the Library's holdings.
If you have a query, please email eresources