# Step Error Messages

> Look up exact validation messages from Combine, Sort, Repeater, list-processing steps, and Human Review.

Use the exact text from the step's Executions tab to find the matching remedy. These messages identify configuration or input that the Step cannot accept.

## "Combine needs exactly two incoming branches"

**Symptom:**
A Combine step fails before it does any work. The message names branches rather than lists.

**The Cause:**
Combine takes one list from each of two connected branches. One branch, or three, and it cannot tell which is which.

**The Fix:**
Count the lines arriving at the step. Add the missing branch, or take the extra one out.

Related: **"Combine must wait for both incoming branches. Set its branch wait mode to AND."** Combine always waits for both of its inputs, so its wait mode is fixed and the chip on it is a label rather than a control. If you see this message, delete the Combine step and add it again to restore its wait mode.

## "First list and Second list must refer to different connected branches"

**Symptom:**
Combine refuses, and both list fields look correctly filled in.

**The Cause:**
Both fields point at the same branch. Combining a list with itself has no useful answer.

**The Fix:**
Open **Second list** and pick from the other branch.

## "Sort needs at least one 'Sort by' row"

**Symptom:**
Sort fails immediately.

**The Cause:**
No rule has been added, so there is nothing to order by.

**The Fix:**
Add a **Sort by** row: a field, a type and a direction. Leave the field blank to compare each whole item, which is what you want for a list of plain values.

Related: **"Limit needs a number of items to keep"** and **"Limit's 'Number of items' must be a whole number of zero or more"** mean the count is missing or is not a whole number. Zero is allowed and returns an empty list.

## "The list was empty, so this loop ran no passes"

**Symptom:**
A [Repeater](/build/action-steps/loops) finished at once. Nothing inside the loop ran, and the step is not marked failed.

**The Cause:**
The list it was given had no entries. That is not an error, and the run carries on from **When finished**.

**The Fix:**
Nothing, if an empty list is possible in normal use. If it should never be empty, look at the step that produced it: a [Filter](/build/action-steps/filter-items) that discarded everything, or a fetch that returned nothing, are the usual reasons.

## "The loop finished but nothing connected back into it"

**Symptom:**
A [Repeater](/build/action-steps/loops) ran, but no results came out of it.

**The Cause:**
A loop turns because the last step of its body connects **back** into the Repeater. Without that returning line, each pass runs and its output goes nowhere.

**The Fix:**
Draw a connection from the last step inside the loop back to the Repeater step.

## "can work on at most 100,000 items at once"

**Symptom:**
[Sort](/build/action-steps/sort), [Limit](/build/action-steps/limit) or [Remove duplicates](/build/action-steps/remove-duplicates) refuses, naming both the ceiling and your list's length.

**The Cause:**
These steps hold the whole list in memory to work on it, and 100,000 entries is the ceiling.

**The Fix:**
Reduce the list before it reaches the step. A [Filter](/build/action-steps/filter-items) that removes what you do not need, or fetching in pages, are both cheaper than trying to process everything at once.

## "approverEmail is required but was not provided"

**Symptom:**
A [Human Review](/build/action-steps/user-approval) step fails instead of waiting for somebody.

**The Cause:**
No approver address, or one that is not a single valid email. A list of addresses is not accepted here.

**The Fix:**
Set one address. If it comes from an earlier step, check what that step actually produced: a field holding several addresses, or an empty one, fails the same way.

## What's Next?

- Find the failing step and its input with [Debug a Run](/reference/debug-a-run).
- Check list and field references in [Data and Mapping Problems](/reference/data-and-mapping-problems).
- Review platform-wide ceilings in [System Limits & Quotas](/reference/system-limits).