If using IDS/ETIS to code keys where the keys have been cleared from PATS memory (adviseable from a salvage auction) you need to pair at least 2 keys to initialise the system.

If just 'adding a key' and not deleting other known keys you can just add 1 key to it.

Some more modern Fords don't allow the old trick of turning key on, off, then adding a blank key they require proper programming.