Why am I seeing "Authentication failed"?

In this case, the connected app is denying access to PieSync, because of any number of reasons:

• A time-out after a prolonged period of inactivity
• The account's password was changed
• The account no longer exists, or had its changed;
• The account no longer fits the required conditions, e.g. as a consequence of a billing issue;
• ... or somewhere along those lines.

Specifically, changes to the account credentials (e.g. changing the password) may be a deliberate safety measure, but naturally, this will prevent PieSync from accessing the contact data any further.  Therefore, you need to re-authorize your app for PieSync to be able to read & write to it.

1. The PieSync connections tab provides an overview of your connections. The ones that need attention will be presented on top.

2. A dropdown list will appear after clicking the connection box, allowing you to reauthenticate the account.