Is more than 1 Keyword Phrase No Longer Possible?

Hello,

Thank you for contacting Rank Math and sorry for any inconvenience that might have been caused due to that.

Please share the code you are entering in your functions.php so we can have a look.

Looking forward to helping you.

Hello,

Thank you for the follow up.

The code you shared is used to show the keyword meta tag in your front end, not to add the keywords you can input.:

For taxonomies(tags & categories), only one keyword is required for the tests and there are no tests on the secondary keywords.

Other posts and pages accept 5 keywords by default. This can be extended to allow more keywords using the following filter:

/**
 * Change the Focus Keyword Limit
 */
add_filter( 'rank_math/focus_keyword/maxtags', function() {
    return 10; // Number of Focus Keywords. 
});

Hope that helps and please do not hesitate to let us know if you need our assistance with anything else.