On the border between Gambia and Casamance via Seleti:

Pass control want to see pre-approved enrollment / approved pre enrolment and payment confirmation incl. email, passport, hotel reservation and flight tickets. You get stamp in the passport and on the enrolment and that's it. When you go back for example to Gambia, you need to show all this documents, get stamp again and it's all. It's rather a quick process.

So it works on other borders too.