Problems with adwords conversion tracking problems

I have problem with adwords conversion tracking:

My project domain A is informational products site, and promoted through adwords. Domain A contains links to products checkout site domain B. So now I want to track sales and lead conversions in adwords.

This is a scenario - PPC -> Domain A -> Domain B (checkout).

I've added sales conversion tracking code on domain B.

Now as I tested by my own adwords is tracking only about 50% conversions, and remarketing tracking is even worse - about 10-20% of conversions.

How can I solve this problem?

You have to add the tracking code on Domain B==>Thank You Page.

The page that you show after successful product purchase.

seosoldier is correct. in my experience, If you dont have a thank you page embedded after the check out process is complete, your measurments will be far less accurate.