Sent email to RC Sport Flyer for clarification as my entry did not work either. Received the following:
You must:
1. Click the U.S./Canada (digital & hardcopy) radio button
2. Click the U.S./Canada Subscribers price of $29.95
3. Enter the code IMAA-Mems in the Discount Code box
4. Click Apply Discount Code
5. Then fill in the rest of the information
6. Do not put in your credit card information.
Please share this information with other IMAA members.

I originally neglected to 'Apply Discount Code.'

All good now.