SOI (Single Opt-In) — the type of offers where conversion is counted when the user leaves his email and/or some data about himself (age, interests, etc.).
SOI-offers seem to be very simple to get conversions. You can make money on them in developed countries where advertisers are ready to pay for clients’ private data. In developing countries, such offers appeared not long ago, and the payouts are quite low.
Despite GEO, the payouts on such offers are the lowest in the vertical. The usual, the simplest the action, the lower payout for the conversion. That is the best option to start in affiliate marketing.