Although fit4NM 3.6.5 does not support NONMEM 7.3, we fixed major bugs in earlier versions of fit4NM.
1. Earlier versions of fit4NM do not work when $SIGMA was absent, for example, in logistic regression. We fixed this bug in fit4NM 3.6.5.
2. With PRED, fit4NM adds MDV to $INPUT in a control file and a MDV column with values set to 0 in a data file. The original control and data files are renamed to *_original.ctl and *_original.csv, respectively.
Fit4NM will support NONMEM 7.3 soon.