Yep, I tested the process myself - tested with both checked and unchecked.
I added the value of the $newsletter in my ZC intro email to discover it was always 0.
I'm not a php programmer but following the logic of the includes/code it appears that another plugin (how_did_you_hear_about_us_v150) had modified this bit of code in the file "tpl_modules_create_account.php"
<?php echo '<label class="m-checkbox m-wrap" for="newsletter-checkbox">' . zen_draw_checkbox_field('newsletter', '0', $newsletter, 'id="newsletter-checkbox"') . ENTRY_NEWSLETTER . '</label>' . (zen_not_null(ENTRY_NEWSLETTER_TEXT) ? '<span class="alert">' . ENTRY_NEWSLETTER_TEXT . '</span>': ''); ?>
<br class="clearBoth" /
I diff'd this with the same file pre-installation version of the same file and saw that 'newsletter', '0' was 'newsletter', '1'
Setting this back to 1 seems to have activated the newsletter subscribes. Not sure what the ramifications of the change I've made will have...
...but I guess that's an issue for the other plugin not this one.
Thanks for your pointer.
Troy.
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