does the 'Reseller' field let you type in something?
If no, are you getting an error when trying to proceed without providing a reseller?
You could try calling our hotline or chat (https://www.fortinet.com/support/contact) to get some assistance with the product registration; the Customer Service team is the one dealing with registration/contract/licencing issues and similar.
+++ Divide by Cucumber Error. Please Reinstall Universe and Reboot +++