Get On The Air — how to add / verify ADIF fields
https://getontheair.app/guide/logging/adif/
Spec: https://adif.org.uk/317/ADIF_317.htm

MY_  = the logging station (you, the activator)
no prefix = the other station (hunter / P2P)

PARKS
  MY_SIG          POTA
  MY_SIG_INFO     US-1356
  MY_POTA_REF     US-1356   or US-1356,US-4516
  SIG             POTA      (them, P2P)
  SIG_INFO        US-0022   (their park)
  POTA_REF        US-0022   (ADIF 3.1.5+ list form)
  MY_SOTA_REF     W3/SV-001
  SOTA_REF        (their summit)

GRIDS
  MY_GRIDSQUARE   your Maidenhead this sitting (6 chars preferred)
  GRIDSQUARE      theirs (lookup, or they said it)

HOW TO GET YOUR GRID
  Phone GPS / Organic Maps / radio GPS / qthlocator.com
  Write it on the field sheet BEFORE CQ
  Do not reuse the home grid for a park 80 miles away

HOW TO GET THEIR GRID
  Callbook (QRZ XML, HamQTH) while you have data
  Polo Full export (NOT the POTA export)
  N3FJP: Fill Fields When Tabbing from Call
  After the fact: Edit > Fill Fields Determined by Call

HOW TO ADD THE TAG IN N3FJP
  Settings > Other Field Titles and Fill Behavior
  Title = exact ADIF tag (underscores, uppercase)
  See n3fjp-other-fields.txt

HOW TO ADD THE TAG IN POLO
  You don't type tags. Add the POTA/SOTA/WWFF activity on the Operation.
  GPS on the operation = MY_GRIDSQUARE
  Their park field on the QSO = SIG_INFO
  Export Full ADIF for grids; POTA export for pota.app

RECAP CARDS
  Map uses MY_GRIDSQUARE (you) and GRIDSQUARE (hunters)
  Empty map = you imported the privacy-stripped POTA file