To sync Haystck contacts with iOS contacts manually (only do this if the automatic way failed), do the following:
Step 1: Open Settings by tapping on the icon from the home screen.
Step 2: Tap to select Accounts & Passwords.
Step 3: Tap on Add Account to proceed.
Step 4: Select Other.
Step 5: Under Contacts, tap to select Add CardDAV Account.
Step 6: Enter the CardDAV account details in the fields for:
- Server: https://webdav.thehaystackapp.com
- User Name: The email address you use to sign into Haystack
- Password: The password for your Haystack account
- Description: Haystack Contacts
Step 7: Tap the Next button. Your iOS device will then verify the credentials and save the new account.
And you're done.