Hi Hana Molina Mohammad. Yes, you can substitute the lychee with longan. However, the taste will be slightly different as lychee has a bit of sour-sweet taste but longan is sweet only. Enjoy!
Hi hmsmedia2005, It's a fruit and it's a close relative between rambutan and longan. The flash are white in color with quite a big seed in the center. Some are sweet and some are sour. You may want to find out more details from Google. Thanks for comment.