If you are having issues with the filter, try pasting the contents into a base64 decoder to see if it is valid. It should display a JSON object e.g. {"t8": [182, 183, ...]}
You can also try to manually copy and paste the filter if the button is not working for you.
Note: This is a HIGHLIGHT filter, not a loot filter. You need to import it in the correct place in the game.