SOI, single opt-in, means a sign-up counts the moment the user submits the form. No confirmation email, no second click. For an affiliate it is the easiest lead to get paid for; for the advertiser it is the least verified one, which is why SOI payouts are lower and quality checks are stricter.
Single opt-in (SOI) is a registration flow in which a user becomes a lead or subscriber immediately after submitting a form. Its counterpart, double opt-in (DOI), adds a confirmation step: the user must click a link in an email, or enter a code, before the registration is complete. In affiliate offers the acronym describes when the payable conversion fires. An SOI dating or sweepstakes offer pays on form submit; a DOI offer pays only after the confirmation.
That one difference shapes everything around the offer. SOI converts more often because there is less friction, so payouts are lower and caps tighter; DOI converts less, but each lead comes with a verified email, so payouts are higher. Advertisers running SOI compensate with checks after the fact: email validation, duplicate detection, comparison of lead activity against the rest of their base and, when quality is poor, scrubbing. A high scrub rate on SOI traffic is the main way affiliates lose money on a model that looked easy.
Outside affiliate marketing the same terms describe how email lists are built. Mailchimp switched its default from double to single opt-in on October 31, 2017, while keeping double opt-in as the default for customers in the EU, because confirmed consent is easier to document under GDPR. That split is a good summary of the trade-off: single opt-in grows a list faster, double opt-in produces proof of consent and cleaner deliverability.
Compliance follows the flow. Under GDPR an email collected through an SOI form still needs a lawful basis and clear information about what the user is signing up for, and the regulation’s recitals state that silence or pre-ticked boxes do not constitute consent. In practice many EU-targeted offers run DOI for exactly that reason, while SOI is more common in markets where consent documentation is lighter or the advertiser accepts the risk.
You send 10,000 clicks of push traffic at 0.15 USD per click, a total cost of 1,500 USD, to two versions of the same dating offer.
| SOI | DOI | |
|---|---|---|
| Conversion rate | 12% | 5% |
| Leads | 1,200 | 500 |
| Payout | 1.50 USD | 4.00 USD |
| Gross revenue | 1,800 USD | 2,000 USD |
| Scrub rate | 20% | 5% |
| Approved revenue | 1,440 USD | 1,900 USD |
| Profit | −60 USD | +400 USD |
The SOI version looked better on day one: more leads, revenue on the dashboard within hours. After scrubbing it is a small loss, while DOI is clearly profitable. Change one assumption and the picture flips: with a 5% scrub rate the SOI version nets 1,710 USD and a 210 USD profit. The scrub rate, not the payout, decides the model, which is why the first question to ask an account manager about an SOI offer is the historical approval rate for traffic like yours.
Every field on an offer page — payout, cap, GEO, flow, KPIs, hold — decides how you get paid or get burned.
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SOI counts the lead when the form is submitted; DOI counts it only after the user confirms through an email link or a code. SOI converts more and pays less, DOI converts less and pays more, and DOI leads are verified while SOI leads are checked afterwards.
Because the advertiser receives an unverified contact and absorbs the risk that it is fake, duplicate or disinterested. The payout reflects the average value of such a lead after quality checks. The volume is the compensation: SOI flows convert several times more often than DOI flows.
It varies by vertical, GEO and traffic source, so there is no universal figure. The useful number is the historical approval rate for your type of traffic on that specific offer, which your account manager can share. Build it into your EPC before you buy traffic, not after.
Sources with cheap clicks and simple intent: push, pop and redirect traffic, SFW social placements and mobile display. The form is short, so the creative does most of the qualifying; the closer the ad is to what the registration actually offers, the lower the scrub.
References are listed as plain text on purpose; look them up by title and publisher. Updated: 2026-10-02.
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