Due to the company's failure to update the cancellation information of the iCard to the immigration system, I was unable to clear customs. I then went to T3 airport to handle the customs clearance myself. (Note ⚠️: Only T3 airport has customs clearance services) The location is at gate 7 of the departure level of T3. Just ask at the main entrance for the place to handle the ECC, and you can directly handle it at the counter for less than 3000p. There's an agent sitting nearby who charges over 5000p to help you fill out the forms, but actually, you can do it yourself. The form filling is very simple and it takes only 15-20 minutes to complete. Then, I departed from T1 airport, and throughout the process, no one asked for tips, probably because the checks have been quite strict recently. I didn't see anyone asking for tips at T3 and T1!

I'm off now, wishing all friends a smooth journey back home. Sharing this because I found it quite confusing on my own.