At this time, it is not possible to pass in dropdowns, sources, assignee IDs, contact types, or any dropdown into Zapier without work arounds. This article will go over a solution.
Add an action called "Formatter by Zapier." Select "Lookup Table." Put your string dropdown or source values on the left and the IDs on the right. It is a lookup table to replace the strings with IDs, as ProsperWorks can only read the ID values at this time.
Here is an example using Sources (zoom in the page to see the images better):
To get the Dropdown or Source IDs, just go to action 3. Create Lead and click sources and it will dropdown with all the IDs:
If you run into any issues or have any questions, please make a request here