Note: Be aware that passing sensitive data to affiliates can enter in conflict with the European GDPR.
If you want to pass metadata along with the basic conversion data, you will first need to enable this in the Tapfiliate tracking code, as explained here.
After that, go to your dashboard, click on 'Programs' > Select the program in which you want to this information to go to your affiliates > Click on the 'Settings' tab > Go to 'Advanced' > On the top of the screen, you'll see option 'Exposed meta data'.
Fill in the field a comma-separated list of the metadata keys that you added to your code, and would like to make visible for your affiliates. This is case sensitive, so make sure your input matches your metadata keys.
Don't forget to hit save!