As resetting the Synology wasn’t a possible solution, re-install the app worked for me.
Works also by using application settings and reverse proxy:
Contacts - reverse proxy:
Calendar - application settings:
I have synced DAVdroid on my Android mobile with CalDAV on my Synology NAS, works great.
Having some difficulty with CardDav however.
If I go into my DAVDroid account which I setup for my calendar I see two sections, one for CalDAV where I have my calendars setup, then one for CardDAV. If I attempt to add a new addressbook under CardDAV the “home set” field is already prepopulated with the url for my calendar and I cannot edit it.
So I setup up a separate account for an address book, select “Login with URL and user name”. Enter url as per https://www.davdroid.com/tested-with/synology/ and username and password and create account.
Oddly the new account has a calendar entry (and includes the calendars I have setup for my other account), nothing for contacts.
What am I doing wrong?
This helped me resolve:
Was not using the correct port