Snap -nextcloud12 -ldap

i have installed nextcloud 12.0.4 with snap on ubuntu 16.04.

I want to active the app: “LDAP user and group backend”

But i can not activate it.
The app is shown in the app-panel, but it is not possible to activate it.

It is not possible to click at “LDAP user and group backend” on the Button “Activieren”

Missing ldap module in php?