[horde] CarDAV not working on iPhone

[INFO - Digital Style Informatica]

CarDAV not working on iPhone

When I put my subscription address on IOS 12 and Horde 5.2.22 it says 
"Verifica dell'account carddav non riuscita" i.e. "the CalDAV account 
cannot be verified"
Going on it save configuration, but it change address removing part 
after domain i.e. "www.test.com/SubscriptionInformationRemovedOnSave"

I do not use SSL, is it necessary?

Any ideas? Thank you.

p.s.

Horde 6.0 is on the way or is a dead project?

Regards