Nafli Itikaf

I read there are three types of itikaf: Sunnah (the one Prophet SAWW practiced), Wajib (compulsory because u made an oath to God in return for something), and Nafli<
I did not understand the concept of nafli itikaf, If anyone has any idea about what it is, how it is performed, and the requirements, can you please explain briefly, TIA

السَّلامُ عليكم ورحمةالله وبركاته

Whenever you enter the mastjid, you can make the intention of Nafl itikaaf, whether you pass through for a moment or stay for weeks. As with other types of itikaaf, you get additional reward and are allowed to eat, drink and sleep in the mastjid (although you should perform some zikr or salah before doing so).

Unlike Sunnah and Wajib, there are no other requirements like not being allowed to leave.

so fasting is not mandatory in nafli itikaf?

No, fasting is only required for Fard and Wajib itikaf.