Why is the Preview & Schedule button greyed out?

This guide covers every reason the Preview and schedule 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 hunting through fields, hover over the greyed-out button — Letterhead shows a tooltip explaining why it’s disabled. Two messages cover most cases:

• “Please fill out the required fields to save and schedule.” — a required field is missing or invalid. Most common cause; see Cause 1.
• “Cannot schedule: the ESP API key is invalid. Contact a company administrator.” — the sending integration on your channel has a credentials problem. Not fixable from the letter; see Cause 5.

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

Cause 1: A required field is missing

On the Preview and schedule step, the right-hand sidebar marks required fields with a red asterisk:

• Email Subject
• Preview Text (also acts as the letter’s subtitle)
• Audience
• Date and Time

If any is blank, the button stays disabled. Filled them all and it’s still grey? Click out of each field once more — Letterhead validates when you leave a field, so a field can look filled but not be registered. Re-hover the button; if the tooltip is gone, you’re good.

Cause 2: Social card text over 180 characters

Custom Social Card fields have a 180-character limit, and an over-limit Title or Preview text shows a validation error. Trim the field — titles are best around 60–70 characters anyway (social platforms truncate), and preview text around 150.

Cause 3: An HTML block has invalid HTML

If an HTML block in your letter body can’t be parsed, scheduling is blocked. Go back to the compose step and look for an HTML block with an error indicator; fix the markup (unclosed tags, missing quotes) or delete the block. See How can I use HTML in Letterhead?

Cause 4: A UTM tracking parameter is invalid

A malformed UTM parameter on your channel’s links blocks scheduling — typically a missing =, an invalid character, or an empty key. Look for an error indicator next to your link settings, or ask whoever manages the channel’s link settings. See Tracking & UTM codes in Letterhead.

Cause 5: The channel’s ESP integration is broken

If your channel’s email service provider API key is invalid, missing, or mismatched, the tooltip reads: “Cannot schedule: the ESP API key is invalid. Contact a company administrator.” This can’t be fixed from the editor — an admin needs to update the credentials in Settings → Integrations.

Cause 6: A/B test isn’t fully set up

If you enabled an A/B test but the second subject line (or another A/B field) is blank, the button stays disabled. Complete the setup or turn the test off.

Cause 7: A save is still in flight

Right after an edit, the button briefly reads Saving… and is disabled until the save completes. If it doesn’t return to Preview and schedule within ~10 seconds, refresh the page (your changes are autosaved) and try again.

Still stuck?

1. Refresh the page — your work is autosaved.
2. Check the browser console for errors (Cmd+Opt+J on Mac, F12 on Windows); screenshot any red error.
3. Contact support with the letter’s Unique ID, the channel, and a screenshot of the scheduling sidebar.