You need to craft an extension for that hook.
https://ellislab.com/expressionengine/user-guide/development/extensions.html
This guide is pretty thorough... did you make sure to install your extension after you made it? If it's not in the
exp_extensions
table, your extensions method won't get fired on that hook. Could you post your extensions contents (here or on a pastie site like pastebin and share) so we can help you? I will edit my answer once I see what you've done so far.
Edit
Here's some changes you need to make to your extension file. First, you have to give your method a name! And you need to allow it to accept the required parameters from the hook, even if you don't use them:
https://solspace.com/docs/user/extension_hooks/#user_register_end
public function my_submit ($user_ob, $member_id)
{
// add code for the user_register_end hook here.
require_once("/base/cleintapps/mysubmit.php");
}
Then you have to make sure you are telling ExpressionEngine to use that method when the hook is called (notice the 'method'=>'my_submit' part):
public function activate_extension()
{
// Setup custom settings in this array.
$this->settings = array();
$data = array(
'class' => __CLASS__,
'method' => 'my_submit',
'hook' => 'user_register_end',
'settings' => serialize($this->settings),
'version' => $this->version,
'enabled' => 'y'
);
$this->EE->db->insert('extensions', $data);
}
And you need to make sure this extension file is called:
ext.send_external_data.php
and lives in this folder:
/your_website_html_root/system/expressionengine/third_party/send_external_data
Depending on how the User module handles hook calls, you might need to add
return;
or
return $user_ob;
after your require_once call inside of that function. Make sure that you disable this extension, make the changes (specifically the 'method'=>'my_submit' part) to this file, and reinstall it via the
Add-Ons -> Extensions
menu in your ExpressionEngine control panel. The extension table has a column called method, and if you don't get your method name in that cell ('my_submit' or whatever you choose), ExpressionEngine won't call your function. Let me know how it goes, and feel free to update your code pastie if it still isn't working, and I'll gladly suss it out for you!