Newbie to this forum and a novice troubleshooter. DavDroid v2.0.4-ose (245) via F-droid Phone: Samsung Galaxy S9 running Android v8.0.0 NextCloud server v13.0.1 This referenced DavDroid error was the Internet search term that brought me to this thread. I don't know how to interpret info from the DavDroid error dump. I was seeing the problem from another client too, though. Thunderbird with Lightning Calendar add-on on my linux laptop. Thankfully the error/warning message in Thunderbird cited a HTTP return code of 415. I was able to look into the server logs for that error and find the specific(in my case it was only one) .ics entry that was causing this error. I'm not sure how others (citing ics entries above) found the offending entries but I share my experience and troubleshooting path in case someone can make use of it. Deleting the entry (appended below) cleared away the DavDroid error for me. This was not a new entry and I don't understand why it would all of a sudden start causing problems but then I don't actually use an Apple device but the person I'm sharing this calendar with does. So, perhaps their client modified the entry(I'm speculating based on the PRODID)? The HTTP status code of 415, "unsupported media type" might offer a clue to someone more clued in about these data formats too. BEGIN:VCALENDAR VERSION:2.0 PRODID:-//Apple Inc.//Mac OS X 10.12.6//EN CALSCALE:GREGORIAN BEGIN:VEVENT TRANSP:TRANSPARENT DTEND;VALUE=DATE:20151108 LAST-MODIFIED:20171031T125845Z UID:84b9619e-a433-44c7-bc8a-f3514903a0d0 DTSTAMP:20171106T145050Z DESCRIPTION:birth year ? X-MOZ-GENERATION:3 SEQUENCE:0 CLASS:PUBLIC CATEGORIES:Birthday X-MOZ-LASTACK:20171031T125845Z SUMMARY:Cousin Jamee's bday! DTSTART;VALUE=DATE:20151107 X-APPLE-TRAVEL-ADVISORY-BEHAVIOR:AUTOMATIC CREATED:20151129T173905Z RRULE:FREQ=YEARLY BEGIN:VALARM X-WR-ALARMUID:816B6585-D97E-4E0D-BBB3-5108CFA9B644 UID:816B6585-D97E-4E0D-BBB3-5108CFA9B644 TRIGGER:-PT15H ATTACH;VALUE=URI:Basso ACTION:AUDIO X-APPLE-DEFAULT-ALARM:TRUE ACKNOWLEDGED:20171031T050001Z END:VALARM BEGIN:VALARM X-WR-ALARMUID:CA946A68-9EAF-4A54-A077-E386E08F0F06 UID:CA946A68-9EAF-4A54-A077-E386E08F0F06 TRIGGER:-P1W ACTION:DISPLAY X-LIC-ERROR;X-LIC-ERRORTYPE=PROPERTY-PARSE-ERROR:Parse error in property name: ACKNOWLEDGED ACKNOWLEDGED:20171031T050001Z DESCRIPTION:Default Mozilla Description END:VALARM END:VEVENT END:VCALENDAR