Is the cost for the WP ADA Compliance Plugin a onetime, annually or monthly payment?

It depends whether you purchase a subscription or flexible pricing plan. WP ADA Compliance Online subscription plans include our WP ADA Compliance Check WordPress Plugin and premium access to our online scanner which can be used to check any non-Wordpress websites. Subscription plans includes unlimited support and updates and must be renewed annually to continuing using the software.  Flexible plans allow you to use the software for as long as you like after paying the one time fee but we strongly recommend that you renew the license at the end of the first year to continue to receive software updates and support for the plugin.