Why the button to start your sync is greyed out

Something on the page isn't finished yet, and the button waits for it. Five different things can hold it, and only one of them is a plan limit.

The button sits at the bottom right of the sync composer and says Start sync. (There's no longer a Continue button — the composer used to be two steps and is now one screen.)

Work through these in order

1. The sync has no name. The name field is near the bottom, under Sync details. It fills in automatically from the calendars you picked, but if you cleared it, or typed spaces, the button stays off. There's a red line under the settings saying so.

2. You picked a custom title and left the text empty. Under Appearance, if the title is set to Replace title or Add a prefix, the text box next to it can't be blank. Type something, or switch the title back to Title says "Busy" or Use original title.

3. An exclusion rule has no value. Under Filters, a "Title contains" rule you added but never typed into blocks the button. Type the word you want to skip, or remove the row.

4. The setup is over one of your plan's limits. This is the one with a message attached — a banner appears above the button naming the limit you hit. Four different limits can produce it:

• your total number of syncs
• how many calendars one sync can hold
• how many calendars you have across all your syncs
• a complexity budget, which counts a sync's size as sources × targets rather than as a flat number of calendars

The last one is why a setup can be refused while you're still under the calendar count.

5. It's already starting. The button reads "Starting…" for a moment after you click. Nothing is wrong.

When the button hasn't appeared at all

The settings only show up once your calendar picks make a workable sync. Before that there's a line telling you what's missing:

• Mirror needs at least two calendars. With one picked, it says so.
• Push needs at least one source and at least one target. One side empty means no settings yet.
• A calendar can't be both a source and a target in the same sync.
• Too many calendars for your plan — it names the number you're allowed.

When Mirror itself is greyed out

You've picked an iCal or ICS feed subscription. Those are read-only — nothing can write to them — so a sync containing one can only be a Push, with the feed as the source. No plan unlocks this. If you want two-way sync with iCloud, connect it as a CalDAV account rather than subscribing to its ICS link.

Switching to Mirror anyway is allowed; it drops the read-only calendars from the selection and tells you how many it removed.

When a calendar is greyed out in the picker

Two reasons, and they look identical until you click.

Another sync already covers this pair. Two syncs writing the same direction between the same two calendars is how you get duplicates, so the second one is refused. Clicking the dimmed row opens a panel naming the sync that already owns it, so you can edit that one instead of building a second.

The account needs reconnecting. That row is properly disabled and won't respond. Reconnect the account under Accounts first.

Known limitations

• A blocked button doesn't always say why. The plan-limit case shows a banner; the blank-name case shows a red line; the empty-rule case shows neither. If nothing is visible, check your Filters rules for a half-typed row.
• The overlap check runs again when you click. The picker greys out what it can see, but the final check happens on the server. A sync built in another tab a moment ago can produce a conflict message at the last step rather than a greyed row.
• Editing an existing sync uses the same button, labelled Save changes, and it ignores plan limits — you can save a sync that's over cap if it was already over cap.