echodrome

This is the output:

array(1) { ["max_links"]=> int(7) }

Which makes me think that PHP has no way of knowing about the values entered on the JS side unless you have a custom table/API that stores this information. There is no way to recreate the JS attributes from the HTML as can be done in the JS side.

@aamirkhatri thank you but that does not seem to provide me with the information I need on save. When I press the publish button the only thing I get adding both your lines is:

Array
(
    [rest_route] => /wp/v2/posts/372
    [_locale] => user
)

the other thing is that this was not posted using jQuery but it seems to be the React library of Guttenberg. Other blocks seem to work by just defining ‘attributes’ in the callback.