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Open the flexbox where you want to place the anchor, keep in mind that it will not work if it is a flex grid and not - it has to be flex.
Add the name of your anchor under 'Linking Possibilities'.
Save.
Go to the menu where you want to have the link. Choose 'use an external link' and paste in the URL to the page.
Add a # in the end of the URL and then paste in the anchor name you added earlier in the flexbox. Remember to remove spaces.
Save and test it! 