Hi Daniel,
NetworkManager does not support unfortunately STA+AP mode. The only way you may make this work is to use the create_ap script from a container (unmanage the interface from NetworkManager). However managing WiFi connection through a container is not something I would recommend, as the OS will not be able to connect to the Internet while the container is not running - that is if the WiFi interface is used as a primary Internet connection. Thus I would advice to attach USB WiFi dongle and split the AP and STA functionality to both the built-in and additional interface. Is that feasible for your project?
Thanks,
Zahari