BI9BSL The requirements for sending to Taiwan are quite strict. You must write "China, Taiwan" as the destination and include the full address in Taiwan on the line below. There should be a small space between "China, Taiwan" and the rest of the address, and finally add "(Recipient:)" at the end.
The postal code from Taiwan should not be written in the top-left corner box; it should be on a separate line below the address.
The sender's address should be written on the upper part of the envelope, in a smaller font, and clearly labeled as "Sender's Address."
In summary, it's a format that falls somewhere between domestic and international formats... And you also need to apply the airline stamp (either self-applied or at the counter).
Also, please note that the minimum postage for airmail letters sent to Taiwan is 10 grams, rather than the usual 20 grams. We recommend using the "China Post Micro-Post" WeChat official account to calculate postage.