When an offer is created in HasOffers, you are asked to create either a Pixel Based Offer (iFrame/Image) or a Postback Based Offer (Postback w/ Transaction_id/Affiliate_id). These two protocols are defined at the offer level and the response from PX or the вadvertiser needs to match this protocol.
If HasOffers accidentally receives the wrong protocol, they will still register the conversion in your Conversion Report but they will reject the conversion and not pay out.
You can override this error by logging into HasOffers and navigating to Company -> Customize Application -> Tracking, then switching Enforce Conversion Tracking Protocols from Enabled to Disabled. This will allow any type of response from PX to be accepted.