'Support all Font Size values' setting cannot be used with an empty Font Sizes configuration.

When I add just a list of numbers, I get

Warning: Undefined array key 1 in Drupal\ckeditor_font\Plugin\CKEditor5Plugin\Font::generateFontSetting() (line 323 of modules/contrib/ckeditor_font/src/Plugin/CKEditor5Plugin/Font.php).

Drupal\ckeditor_font\Plugin\CKEditor5Plugin\Font::generateFontSetting('6
9
12
16
24
32
48
64', 'size') (Line: 184)

I'm having the same issue. I cannot add any font sizes. I've tried the following formats without the ordered list (of course):

• 10px|10px 10
• 10px|10 10
• 10px|10
• 10px|10 Ten

I get the same error every time even though I have toggled on "Support all Font Size values" or not:

'Support all Font Size values' setting cannot be used with non-numeric Font Sizes configuration.

Did somebody got this solved?

I got this resolved by following all the instructions in the README.txt file:

Local installation (non-composer):

    1. Download the CKEditor font plugin (v4.13.x to be compatible with Drupal
       9) from http://ckeditor.com/addon/font.
    2. Place the plugin in the root libraries folder (/libraries or 
      /libraries/ckeditor/plugins).
    3. Install as you would normally install a contributed Drupal module. Visit
       https://www.drupal.org/node/895232/ for further information.

Composer installation:

    1. CKEditor Font Size and Family's composer.json will automatically install
       the library into `base_path()/libraries/font`. To add the library,
       type `composer require drupal/ckeditor_font` at your Drupal project root.

Create a config.js file in the modules/contrib/ckeditor/vendor and add this line:

config.extraPlugins = 'font';

And then add the font families (at /admin/config/content/formats/manage/full_html) and font sizes as instructed in the examples:

Verdana, Geneva, sans-serif| Verdana Font
Lucida Console, Courier New, monospace|Lucida Font
Times New Roman, Times, serif|Times Font

10px|Normal Size
20px|Medium Size
30px|Whopper Size
123px|Size label

Some screens:

I'll update the README.txt to add these extra instructions, for now I'll close this as "Fixed".

Please note that this module is deprecated in favour of the ckeditor5_plugin_pack → module