The validate function would be a great solution – however, this custom field is injected in the user registration form, so it doesn’t seem to trigger the validation functions.
I could be wrong (maybe misconfigured function) but if I’m right, you might want to consider hooking your validation function into the registration form, since adding fields to the user_form = registration is a built-in feature of your system.
I was able to validate the field (and trigger the native WP registration errors) through the registration_errors() hook. However, that brings me to a different problem.
When I var_dump the $_POST variable in this function, it includes the data I want, but it’s attached to an obscure field_ key:
array(10) {
["user_login"]=> string(11) "johnsmith"
["user_email"]=> string(23) "[email protected]"
["_acf_post_id"]=> string(6) "user_0"
["_acf_nonce"]=> string(10) "8294e063ae"
["_acf_validation"]=> string(1) "1"
["_acf_ajax"]=> string(1) "0"
["_acf_changed"]=> string(1) "1"
["acf"]=>
array(1) {
["field_5999b7f405d29"]=>
string(11) "Candlestick Maker"
}
["redirect_to"]=> string(27) "https://example.com/welcome"
["wp-submit"]=> string(8) "Register"
}
I can validate that field (in your solution, check against “not allowed”). But I’m unclear on how to access this field_ key value (in this case, “field_5999b7f405d29“). I can do a var_dump like this and see it, I could reverse engineer it from the database, but is there a way to get that key that’s more intuitive and portable?
* Note the user_ ID is not established at this point, so I can’t, for example, access the field like so:
get_field('occupation', 'user_22');
