Licensing requirements for ODT Rentals Power App are:

Power App License for "Per App"

https://docs.microsoft.com/en-us/power-platform/admin/about-powerapps-perapp

+ A capacity login for external users for the number of portal login users per month.  (day passes per authenticated user)

https://docs.microsoft.com/en-us/power-platform/admin/capacity-add-on#can-i-use-model-driven-apps-by-consuming-app-passes


After purchasing, the Power App license must be assigned to the related environment's capacity.

https://docs.microsoft.com/en-us/power-platform/admin/capacity-add-on#can-i-use-model-driven-apps-by-consuming-app-passes


https://docs.microsoft.com/en-us/power-platform/admin/capacity-add-on#can-i-use-model-driven-apps-by-consuming-app-passes