GxE intreactions in PLINK

hi, I'm trying to do GxE interactions in PLINK. and mycov.dat file is formatted like this

FID   IID          Age    BMI
1     subject 1    66     23.10
2     subject 2    76     25.30
3     subjet 3     32     24.90
5     subject 4    70     24.00

I had some suggestions to do cut off of BMI and code like 0/1 or 1/2 . I have tried both ways i.e, with binary and with continuous. but PLINK keeps giving me the same error "Can only use --gxe option with continuous phenotypes"

Can anyone help me with this? or if there is any other function in PLINK that I can use to do SNP-trait association interactions?

Thanks