A conversion did not count

Go through these in order.

1. Is it in Conversions › Failed? Every refused conversion is there with its reason: hit_expired (the visit was older than the attribution window), invalid_hit (the hit was cut or changed), conversion_type_not_on_offer and the others in Error codes.
2. Did the visit arrive as a hit? Find it in Performance › Hits by partner and time. No hit: the tracking tag is not on that page, or the link is not the partner's. A hit marked not counted says why.
3. Does the offer have that goal? The conversion type your site sent (for example sale) must be a goal on the offer.
4. Was it a repeat? The same externalId counts once; a goal set to once allows one conversion per hit.
5. Is it waiting? Pending, On hold and Quality control conversions count once they are approved. On hold moves on by itself when its time ends.
6. Still not there? Use Settings › Developers › Test integration to make a test hit and send its conversion, and compare it with what your server sends.