If you want to use your own Opt-In form you have to keep the following things in mind:
First, it's absolutely necessary to set the constant "FIELDVAR_PREFIX" to an empty string or this prefix will automatically added to the field name of your form
In order to do so, open the file “default_settings.php” in the “optinssm/config/”-folder, locate the FIELDVAR_PREFIX constant and change it as follows:
After creating your own form you have to adjust the “user_config.php” as descibed in Tutorial: How to include the Opt-In form and to add your fields to the “optinssm_fields”-array.
At last set your form "action" to “./optinssm/php_scripts/opt-in.php" or the link to the "opt-in.php"-script, if the folder was renamed or is located in another directory.
After that set "method" zu "post":
Now your form should be able execute the SmartSerialMail Opt-In scripts and to redirect the SmartSerialMail subscriptions correctly to your SmartSerialMail inbox.