Depending on an offer, conversion usually comes with a delay - the more difficult flow the more time it will take for conversion to come. If offer requires various confirmation, for example, call from call center, keep in mind working hours of the call center and difference in timezones.

Advertiser may take additional time to check and in some cases cancel the conversion if he considers it as a fraud/fake/empty and not willing to pay for it.

Always make sure that you have completed all the terms of the offer. There are offers type like CPI+CPS, and conversion will only count when both conditions are completed.

For subshunter offers conversion will not count if user allowing subscription is already in subscribers base.

Always check offer status before working with it - if it is paused advertiser will not count any conversion.