FerPath is an option for FerRunScript and
other functions of the Fermat interface and multiple other Fer*
functions. It specifies the full path to the Fermat binary.
If set to Automatic, Fermat binaries are expected to be located in
FileNameJoin[{$FeynHelpersDirectory, "ExternalTools", "Fermat", "ferl6", "fer64"}]
and
FileNameJoin[{$FeynHelpersDirectory, "ExternalTools", "Fermat","ferm6", "fer64"}]
for Linux and macOS respectively.
Overview, FerSolve, FerRowReduce, FerRunScript.