If you have an existing InboundWriter account and your WordPress administrator email address matches then you'll be able to use the same account between the web application and the plugin. We did this so that these could be shared. If your administrator email is different then you have a few choices. (a) you can create a new InboundWriter account that will apply to the new address or (b) change your admin email address in your WordPress instance to match your existing account.
We didn't want to create a bunch of orphan accounts and make it harder for existing users to install and use the plugin, especially if they were already paying users.
If you have any further questions let me know. We can also be reached at firstname.lastname@example.org.