Agency_Portal_Email_Settings - Registers settings, renders form fields, manages configuration for both reminder and overdue tabs Agency_Portal_Email_Relay_Compositor - Receives webhook triggers, composes email with placeholders, dispatches (handles both types) Agency_Portal_Email_Scheduler - Orchestrates mission creation on external server when invoice created/modified, manages both reminder and overdue rules Settings page uses standard WordPress settings API: Settings registered via register_setting() under 'portal_invoice_payment_overdue_email_settings_group' Fields rendered via add_settings_field() Email body uses wp_editor() WYSIWYG editor Time selector uses dual dropdowns for hour and minute Numeric fields for interval and stop conditions use simple number inputs Hook Type Purpose