Android 6 & nc15 ... no caldav etc

Dear All,
I am in Westafrica and we want to set up a nc for an entrepreneur group … challenges weak smartphones with max android 6 …
I tried with my android9 and everything is fine … but i need a solution for the others…

we tried the caldav sync adapter from the playstore but it is not goingt through to the account. guess they have some protocol-communication-issues

are there any hints?

Try DAVx from FDROID ( That works for me with Android 6.1 .