I found this much from GRT :
To import a flight plan (any GPS format)
from flight planning software on a USB
stick:
1. From any MAP page press any
button
2. Press NEXT (more than once may be
required)
3. Press PLAN
4. Press right knob and scroll to select
IMPORT
5. Press button labeled UP or DOWN to
select the desired flight plan
6. Press the button labeled LOAD to
copy it to the GRT Sport
I then found this:
In iFly EFB, after creating a flight plan, click More Options, then Share/Export Flight Plan ...
You then choose either Share to Local Network or Export to Shareable file
GRT wants the plan on a USB stick, so file it is. It creates an xxx to zzz.fpl file.
I'll try this next time I go airport hopping.