# Why does my spreadsheet show an "illegal characters" error?

> Learn how to resolve the "illegal characters" error in SecureMailMerge caused by forbidden symbols in your spreadsheet column headers.

## What This Error Means

When you upload a spreadsheet, SecureMailMerge checks that your column headers do not contain certain character sequences. If any column header contains one of these sequences, you will see an error listing the affected columns.

## Which Sequences Are Not Allowed

The following sequences cannot be used in column headers:

- `$$`
- `{{`
- `}}`
- `{%`
- `%}`

## Examples

| Problematic header | Fix |
|--------------------|-----|
| `Price $$` | `Price USD` or `Price (dollars)` |
| `{{Name}}` | `Name` |
| `Notes {%raw%}` | `Notes raw` |

## How to Fix It

1. Open your spreadsheet in Excel, Google Sheets, or another editor
2. Rename any column header that contains a forbidden sequence
3. Save the spreadsheet and upload it again in SecureMailMerge

Only the **header row** (the first row) is restricted. The data rows below can contain any characters without issue, `$$`, `{{`, `}}` and so on are perfectly fine in cell values and will merge into your emails as-is.

## The Error Message

When this validation fails, you will see a message similar to:

> The following column headers contain characters that are not supported: "Price $$" contains $$; "\{\{Name\}\}" contains \{\{, \}\}.
> Column headers cannot contain: $$, \{\{, \}\}, \{%, %\}.
> Please rename the column(s) in your spreadsheet and try again.

The message lists every affected column and which sequences were found, so you know exactly what to rename.