Don’t forget to add the strings to the Strings Translation dashboard first.

So go to WPML > Strings Translation and go to the bottom of the page.

Click on the link.

Then you will be shown a bunch of strings which are categorized.

You will need to select them (checkbox) then go to the very bottom of that page and click on Import Strings.

Then you will see them in the WPML > Strings Translation dashboard.

If you still have trouble please send me the admin login credentials for the site so I can log in and have a look.