EFIN (Electronic Filing Identification Number)
In short
An EFIN is the identification number Indonesia's tax office issues so you can file your SPT Tahunan online through e-Filing instead of submitting it on paper.
You request an EFIN once, in person or through the DJP's supported channels, after you already have an NPWP. Keep it safe — you will need it every year to log in and submit your SPT Tahunan online, and losing it means going through a recovery process before you can file.
This is general information only, not tax or legal advice — confirm the current request and recovery process directly with the DJP or a licensed Indonesian tax professional.