As of Avenza Maps 3.5 (which was released in May 2018) users can import as many maps as they wish, but if they’re using the free version of the app then only the first 3 maps you import will be active. If you have more than 3 imported maps then the rest will be inactive.
If you’d like to have more than 3 maps active, you’ll have to purchase a subscription. The Plus subscription (previously called ‘Unlock Map Imports’) is for recreational use and allows unlimited active maps. The Pro subscription is for all non-recreational use of the app, and includes Pro features such as unlimited active maps, shapefile support, and other Pro specific features. Subscriptions can be purchased in-app by going to Settings > Upgrade Account.
Maps from the Avenza Map Store are unlimited and maps can be free or purchased at a cost. You can look for maps in the Avenza Map Store by going here.
If you have any other questions let me know.
Avenza Systems Inc