Just tested and works fine
Here’s what I did:
1) Create an ACF text field called Random String
2) This creates the label random_string
3) For testing, I assigned this field to User Role is equal to All
4) I added the below code to my functions.php file:
<?php
add_action( 'user_register', 'myplugin_registration_save', 10, 1 );
function myplugin_registration_save( $user_id ) {
####generate the random number
#get current date/time
$date = date('YmdH:i:s');
#randmoise
$randomise = ($date * 25);
update_user_meta($user_id, 'random_string', $randomise ); #change random_string to your ACF field label!!!
}
5) I registered a new user
6) I then clicked to edit the user, scrolled down to my new Random String field, this was the result: 50527810375
Code and entire process tried and tested!
