TL;DR
If your campaign shows Active but nothing is sending and leads show a "send user missing" error, re-assign the campaign's original sender (the sender selected before the campaign was first launched) in the Sequence tab. Leads unstick and sending resumes within a few minutes. Until the original sender is restored, the leads stay stuck.
Symptoms
Campaign status shows Active, but no emails are going out.
Leads are stuck and don't move to the next step.
A red triangle with "send user missing" appears when you hover over affected leads.
Leads sit "in progress" but never send Step 1 (or the next step).
The problem started right after you changed the sender on an already-launched campaign.
Environment
Applies to campaigns that were already launched when the sender was changed.
Affects leads that were launched under the original sender (the one assigned before launch).
Step-by-Step Fix
Step 1: Open the affected campaign
Go to Campaigns and select the campaign that is stuck.
Step 2: Open the Sequence tab
In the campaign, open the Sequence tab to view the email step settings.
Step 3: Re-assign the original sender
In the email step, open the sender dropdown and select the original sender — the sender that was assigned before the campaign was first launched.
✅ Verify: The sender field displays the original sender's name.
Step 4: Restore the original LinkedIn sender (if applicable)
If the sequence includes LinkedIn steps, click the LinkedIn step and re-select the original LinkedIn sender in the same way.
Step 5: Confirm the change saved
The sender change applies as soon as you select it. No separate save is needed.
End state: The stuck leads resume, the "send user missing" error clears, and sending continues under the original sender.
Confirm It's Fixed
✓ The "send user missing" error no longer shows on the affected leads.
✓ The campaign is Active and leads move to the next step.
✓ New sends appear in the campaign activity within a few minutes.
Why It Happens
Root cause: Sender assignment is locked at launch time. When you change the sender in the middle of a running campaign, leads that were already launched still point to the original sender. Because that sender is no longer assigned to the step, those leads can't send and show the "send user missing" error — even though the campaign still shows as Active.
Prevent: Change the sender before launching, or only between launch batches. Avoid switching the sender while leads are mid-sequence.
Alternatives
If you actually want these leads to move to a new sender permanently (not restore the original), you must relaunch them under the new sender — restoring the original sender only unsticks them under the original. See Change the sender for a campaign for the relaunch flow.
Escalate If Unresolved
If leads stay stuck after restoring the original sender, contact lemlist support and include:
The campaign name or URL, and the original sender's email address.
Whether the original sender's account shows as connected in Settings → Email Accounts.
A screenshot of a stuck lead showing the "send user missing" error.