If you have multiple domains pointing to just one website, then just 1 IDX license would be needed.
If you have multiple websites, each website would have its own IDX search and client management system but can be managed under one account.
There is an additional cost for having multiple websites on an account. Visit here to learn about the pricing.
How to Add Another Website to my Account
You can create a website in your Agent Admin under the 'websites' page. This website will remain in 'pending' status until activated by our team. In some cases, your MLS may require additional paperwork to be completed for each website you wish to add. You will need to contact us to complete the activation of this site at firstname.lastname@example.org.