Yay solved it :) if anyone else needs to send parameters in a url string here is an example how I have approached it:
<a href="//example.com/api/getData?id={$ID}&date={$C_Date}&name={$C_Name}">Add</a>
I placed this in the success section in a custom action.
You can access the fields by clicking on 'Formula Options' and selecting the desired fields on the 'Fields' tab.