Server-to-server postback URL is the most secure and reliable method of counting conversions. Use the URLs which you can see on the 3-rd step of creating campaings to pass conversions from affiliate networks. To get your postback links working you have to:
Include the {token} parameter in your offer's URLs. For example, you can add ?token1={token1} to the offer's URL to have the click ID passed to the postback via the Token parameter on the affiliate network/advertiser side.
Copy-paste the postback URL to your affiliate network panel. Make sure to replace the YOUR NETWORK TOKEN with #s2# if your affiliate network uses the Cake platform or {aff_sub2} if they use HasOffers. Ask your affiliate manager for the relevant token if the network uses a custom platform. Below is what your postback URL will look like on a HasOffers based network:

http://xxxx.adsb4all.com/trackpixel/track?tid=YOUR_NETWORK_TOKEN&amt=REPLACE&txid=REPLACE&cdata=YOUR_CUSTOM_DATA