To apply for Pag-IBIG online registration, visit the official Pag-IBIG Fund website and look for the online registration link. You'll need to provide some personal information such as your name, date of birth, and contact details. After filling out the form, submit it and wait for a confirmation email with your membership ID. If you encounter any issues, it's best to reach out to Pag-IBIG's customer service for assistance or check their guidelines on the official website.