Why is the Preview & Schedule button is greyed out?

This guide covers every reason that button can be disabled, in order of how often you’ll see them, and how to fix each one.

Start here: hover the button for a tooltip

Before you start hunting through fields, hover your cursor over the greyed-out button. Letterhead surfaces a tooltip telling you why it’s disabled. Two messages cover most cases:

• “Please fill out the required fields to save and schedule.” — One of the letter’s required fields is missing or invalid. Most common cause. See the next section.
• “Cannot schedule: the ESP API key is invalid. Contact a company administrator.” — The email sending integration on your channel has a credentials problem. Not something you can fix in the letter — flag it to whoever manages your company account.

If the tooltip says nothing or just shows “Saving…”, the button is temporarily disabled while a save or other request is finishing. Wait a few seconds and try again.

Cause 1: A required field is missing

This is the most common reason. Every letter needs four pieces of information set before it can be scheduled.

Required fields to check

Open Step 2 of 3: Preview and schedule and look at the right-hand sidebar. The required fields are marked with a red asterisk:

• Email Subject — the subject line of the email
• Preview Text — the short snippet that shows in the inbox preview (also acts as the letter’s subtitle)
• Audience — which segment to send to
• Date and Time — when the letter should send

If any of these is blank, the Preview & Schedule button stays disabled. Fill in every red-asterisk field and the button will activate.

Quick check

If you’ve filled in all four and the button is still greyed out, click out of each field one more time. Letterhead validates on blur, so a field can look filled but not yet be registered. Then re-hover the button. If the tooltip is gone, you’re good to go.

Cause 2: Social card headline or preview text is over 180 characters

If you set a custom social card (Step 2 → SOCIAL CARD), each text field has a 180-character limit.

How to spot it

The Title or Preview text field under the SOCIAL CARD section will show a validation error.

Fix

Trim the offending field to 180 characters or fewer. Title is best around 60–70 characters anyway (most social platforms truncate beyond that), and preview text around 150.

Cause 3: An HTML block in your letter has invalid HTML

If you’ve added a custom HTML block to the letter body (in Step 1 → Create), and that block’s HTML can’t be parsed, the Preview & Schedule button is disabled until the HTML is valid.

How to spot it

Go back to Step 1: Create. Scroll through your blocks and look for an HTML block with an error indicator on it.

Fix

Either fix the HTML inside that block (check for unclosed tags, missing quotes, or syntax errors) or delete the block.

Cause 4: A UTM tracking parameter is invalid

If your channel has UTM tracking parameters set on its links and one of those parameters is malformed, the letter can’t be scheduled.

How to spot it

This usually shows up as an error indicator next to your link settings in the channel admin or in the letter’s link block.

Fix

Fix the UTM parameter — typically a missing = sign, an invalid character, or an empty key. If you can’t find it, ask whoever manages the channel’s link settings.

Cause 5: The channel’s ESP integration is broken or mismatched

Your channel sends through an Email Service Provider (Letterhead, Mailchimp, etc.). If that ESP’s API key is invalid, missing, or doesn’t match what the letter expects, scheduling is blocked.

How to spot it

The hover tooltip says: “Cannot schedule: the ESP API key is invalid. Contact a company administrator.”

Fix

You can’t fix this from the letter editor. Reach out to whoever manages the company’s integrations — they’ll need to update the ESP credentials in Settings → Integrations.

Cause 6: A/B test isn’t fully set up

If you’ve enabled an A/B test on the letter (testing two subject lines, for example) and the second version isn’t filled in, the button stays disabled.

How to spot it

You added Subject A but Subject B is blank, or one of the A/B fields hasn’t been completed.

Fix

Either complete the A/B test setup or turn the A/B test off.

Cause 7: A save or other request is still in flight

If you just made an edit, Letterhead may still be saving in the background. The button text briefly becomes Saving… and is disabled until the save completes.

Fix

Wait a couple of seconds. If the button doesn’t return to Preview and schedule within ~10 seconds, your browser or connection might be stuck — refresh the page (your changes are autosaved) and try again.

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Still stuck?

If you’ve worked through all eight causes and the button still won’t click:

1. Refresh the page (your work is autosaved).
2. Check the browser’s console for errors (Cmd+Opt+J on Mac, F12 on Windows) — if there’s a red error, screenshot it and include it in your support ticket.
3. Reach out to support with: the letter’s Unique ID, the channel it’s in, and a screenshot of the right-hand sidebar in Step 2.