Hello Joe,
The button uses JavaScript to duplicate a row to the form.
Your screenshot indicates that there are no rows at all in the table. Normally the plugin forces you to keep at least one market (you cannot delete the last one).
Try this:
1. deactivate the Exchange
2. unistall it
3. install the exchange again and activate it (this will populate the table with one row).
Let me know if this didn’t work. Also, if the above solution did not work, please tell me the following:
1. are you on a multisite WordPress installation?
2. If so, is the plugin network activated or not?
3. Do you see any errors in your JavaScript console when you are the Markets settings page?
with regards