@FG8OJ has made an excellent guide of working GreenCube digipeater with IC-9700 and supporting software. I will not write a new guide as Burts guide fully covers everything.
Valid exchange messages for a QSO should be:
You can look at FT8 needed exchange : 2 exchanges from each side:
A:Grid
B:Report
A:R + Report
B:RR73
or
A:Report
B:R + Report
A:RR73
B:73
