I used “Add account/Login with URL and user name” and entered the URL https://caldav.calendar.yahoo.com and my full Yahoo email address and password. The Yahoo account has “Allow apps that use less secure sign in” enabled. After hitting “Login”, I get “Couldn’t find CalDAV or CardDAV service.” I checked email and password twice, I also tried my Yahoo user name (without @yahoo.com): same result.
The logs are here: https://paste.fedoraproject.org/paste/Xl6e~vhru421jr8MppITcA
Thanks
I have exactly the same issue.
I searched for an application synchronizing Yahoo Calendar with my mobile calendar, with read/write both ways.
Happy to find CalDav where it is written: “Yahoo Mail!” in https://www.davdroid.com/tested-with/
I also noted that they say that : “CardDAV is not supported by Yahoo! (anymore), so please don’t use it with DAVdroid.” (https://www.davdroid.com/tested-with/yahoo-mail/)
Great ! Because I use CalDAV as per Yahoo’s procedure…
So I just bought CalDAV 30mn ago, and followed the steps as described both in the manual, and in Yahoo : https://help.yahoo.com/kb/new-mail-for-desktop/sync-access-calendar-multiple-devices-applications-sln4707.html?impressions=true
I received exactly the same message as Mike, using the same initial procedure.
I tried also by using the login/pwd option. Idem.
here is what I could copy from the debug:
0_1541186800238_BEGIN DEBUG INFO.txt
Less than 2 hours. Better to cancel the purchase now …
I know that Yahoo has always been a pain in the x with their systems, but it seems that no one is currently able to process well their garbage calendar…
pity, I am sure Google calendars are esy to interface with androids calendars, but I would love to stay away from them… (sighs …)
@jprc Did you go to Yahoo “Account info” / Account security and enable “Allow apps that use less secure sign in”? Or maybe there’s a problem with your username/password. Your logs indicate an authentication problem:
2018-11-02 19:30:58 985 [ui.setup.DavResourceFinder] PROPFIND/OPTIONS on user-given URL failed
EXCEPTION at.bitfire.dav4android.exception.UnauthorizedException: HTTP 401
at at.bitfire.dav4android.DavResource.checkStatus(DavResource.kt:273)
at at.bitfire.dav4android.DavResource.checkStatus(DavResource.kt:259)
@rfc2822
thank you for your answer.
Concerning the login username/pwd, I am 100% sure as I did it 3 times, and took a printscreen of both in clear, with copy/paste for the 2nd try, and use a screen recording for the 3rd time showing that I typed the login data as expected - for being 100% that I was not typing something wrong, which can always happen …
Now, concerning "Yahoo “Account info” / Account security and enable “Allow apps that use less secure sign in”.
I do not know what it can be, as I have currently this in my account and have nothing looking like “Allow apps that use less secure sign in”:
@jprc I see you have two-step verification activated. You probably have to generate an app password for DAVdroid and use this password to login with DAVdroid. Does that work?
mmmhhh…
I see… the last option at the bottom ? I never noticed it, or needed it either before today.
I guess I should choose “Other App”…
I will try probably this week-end, and first try understanding how it works (generate a pwd for putting it where?..).
But for that, I will have to re-purchase the app as it has been removed from my library by play.google
I will keep you informed of my tries, success or failure. Thank you very much for your inputs!
@jprc said in Yahoo: Couldn't find CalDAV or CardDAV service:
I will try probably this week-end, and first try understanding how it works (generate a pwd for putting it where?..).
You will have to use this password together with your Yahoo email address in DAVdroid instead of your real Yahoo password. See here for more information: https://help.yahoo.com/kb/SLN15241.html?guccounter=1
I have now updated https://www.davdroid.com/tested-with/yahoo-mail/ for two-step verification. Can you give it a try and tell me whether it works for you?
In short : IT WORKS !!! 
long story below, in case the steps by steps can be useful to another Yahoo user (sorry for my pidgin English…)
Don’t be afraid ! It will look long and complicated, but when you actually do it, it is very very simple: I have simply detailed each and every steps (surely too much…)
This step-by-step is for any one using a two-step verification for your Yahoo Account security.
Your Yahoo Account Security shows your current status. It indicates in my case that the 2-step is activated: you will need then to generate a special password that ONLY DAVdroid will be allowed to use.
When you click on “Generate app password”, a pop will ask you to select your app.
Go at the bottom and choose “Other app”
… then type a name. For easily remembering, I simply type “DAVdroid” (but it is up to you, it does not matter as it is only for your eyes).
When done, click on “Generate”
A password is generated by the system. Here, it is “aaaa bbbb cccc dddd”.
Beware, you can have spaces like in the example below (I had). Password must be used with the spaces, exactly as displayed.
Click on “Done”
My DAVdroid special privilege in Yahoo is with status : “Not used yet” …
You have instructed Yahoo to keep an eye on ANYTHING that will log in, using this password, and as soon as this login is detected, it will be attached to the application registered with name DAVdroid.
We have finished for now with Yahoo
Let’s go to the smartphone, install the app if not done yet, and run it for the 1st time.
Click the big “+” bottom right.
There are 3 options. Choose the classic one : “Login with email address”.
Click on “LOGIN” bottom right.
Now type your yahoo email address, the one in which you have your calendar. Here, MyDog@yahoo.com
… AND TYPE THE PASSWORD YOU GENERATED, NOT YOUR REGULAR YAHOO PASSWORD. (aaaa bbbb cccc dddd in my example)
Click on “LOGIN” bottom right.
Retype your yahoo email adress, and click on “CREATE ACCOUNT”
DAVdroid creates the account, and checks if your configuration can be an issue to the background synchronizations.
I have a Huawei (P20 lite), and it seems some brand can be capricious. Fortunately, the warning were just warnings in my case, and nothing was blocked in the background.
But I had, by instance, to authorise my “battery saving mode” to be disabled for this application (there is a message asking the authorization to do so).
ET VOILA !!! DAVdroid has created my account, and after selecting this account…
… I see that it is all set, I can select and activate MyDog’s Calendar , and start the synchronization !!!
Back in my Yahoo Account in my PC, I refresh the page and receive the confirmation that the special login (with the generated password) is now linked to my app, and Yahoo has it in its records.
Now the final test : I create an event in my PC, and another one in my Android smartphone.
It works in my PC and inside Yahoo : event created at 14h from my smartphone has been correctly transmitted by DAVdroid to Yahoo Calendar…
… and idem in my smartphone : my calendar has received the event created at 12h in my Yahoo Calendar, in my PC
Is not it great ? 
@jprc Thanks for sharing the whole process, including screenshots! I’m happy that it now works for you.
