NB you need to pay $1 per day at the Lafise Bank. Go there first, left hand quick queue, and ask for a 'código 40'. Make sure it's got your name which matches the import document.
Then make a copy (I'd get 2 to be safe). Go back past customs and take first right. There's a couple of copy shops a few metres down on other side of road.
Back in customs get a ticket (Caja option) from the computers by entrance and wait on right for your number to be called. Need licence, title and passport.
Then you need to come back tomorrow (in the afternoon for me, despite doing it in the morning).
There's a beautiful spot to camp about 20 minutes to the south (Casa Inti - on iOverlander) of you need to stay overnight.
Place: DGA Nica
Visited: May 31st, 2017
Location: 12.15112, -86.23312