A voice campaign starts with a list: the customers your AI voice agent will call. Many teams keep that list in a spreadsheet with thousands of rows. As of November 6, 2026, HellouOne imports voice campaign contact lists in the background. The upload returns right away, the campaign wizard shows how the import is going, and when a file cannot be used, the wizard tells you why, right under the file field. The change is live in production.
This is for campaign admins who build voice campaigns from CSV or Excel files. You can keep working while a large list loads, and when something is wrong with a file, you see the reason instead of waiting or guessing.
What was going wrong
Until now the whole file was read and saved while the upload request was still open. Small lists were fine. Large Excel files, from roughly ten thousand rows, could take longer than the request was allowed to run, so the wizard showed a generic server error. Worse, each attempt left an empty draft behind, so a retry or two filled the campaign list with empty copies of the same campaign.
What changes
The upload returns at once and the import runs in the background. The wizard shows a status line while the contacts are imported and while their phone numbers are checked, then the final contact count.
Excel files are read much faster. A file of about 12,000 rows now takes around a second to read, where it used to take several.
If a file cannot be used, the reason appears under the file field. Examples: no phone column, an old .xls file, an .xlsx that is not a valid Excel file, or a file that is too large.
A failed or repeated import saves into the same draft, so you no longer end up with empty duplicate campaigns.
While an import runs, the wizard locks the file field and the View contacts, Create and Save draft buttons, so a second file cannot replace the first halfway through.
Preparing your file
Use .csv or .xlsx. Older .xls files are refused; open them in your spreadsheet tool and save them as .xlsx or CSV.
Include a phone column. Headers such as phone, telefono or teléfono are recognized.
Keep the file to a reasonable shape: up to 256 columns and up to two million cells in total. A typical contact list is far below that.
If the wizard reports a problem, fix the file and upload it again in the same wizard. The error clears and the same draft is used.
Replacing the list on a draft
When you edit a draft campaign that already has contacts and upload a new file, HellouOne asks you to confirm that the new file replaces the current list. If the new file is refused, the old list stays exactly as it was, so a bad upload never leaves a draft without contacts. A campaign also cannot be launched while its import is still running, and an import that stalls is stopped automatically after an hour so the draft does not stay stuck.
How it works with HellouOne
Voice campaigns are how HellouOne's AI voice agents reach a list of customers: reminders, collections, surveys, lead follow-up. The contact list is the first step of the campaign wizard, and everything after it depends on it, from the rounds of calls that follow up automatically to the campaign reports and CSV exports you read at the end.
Contacts imported for a campaign are checked before any call is made, and campaigns that need to wait for the right person keep doing so. If you load campaign contacts through the API, the upload now answers at once and you read the campaign's import status and any import error afterwards; the details are in the HellouOne documentation. For your team, the change is simple: upload the file, keep working, and read the result in the wizard.
