Number of reka’t in Isha Prayer
4 gair muakkadah
2 sunnat muakkadah
= 17. Reka’t
4 reka’t farz is Obligatory and try to Pray with congregation as far as possible because it has 27 times more reward than paying individually.
3 reka’t Witr is strongly recommended but it is not obligatory Prophet Muhammad ﷺ always used to pray this prayer and as for my knowledge of authentic teaching of Prophet Muhammad ﷺ, he never missed it.
2 reka’t sunnat muakkadah is also strongly recommended but it is not obligatory Prophet Muhammad ﷺ always used to pray such prayer
if a person is busy too much, has to go somewhere or any other genuine reason due to this if he or she leave it then upon him there is no sin
4 reka’t gair Muakkadah and 2+2 Nafil, are upto the choice of person
If he or she pray it he will be rewarded but if they leave it there is no sin upon them
Please share with others it will be on going charity for you