Customer "external ID" and matching on import

Each customer in Sliptree has an optional external ID field. It's a free-form string — usually the ID this customer has in another system you use (a CRM, ERP, accounting tool, or spreadsheet). Sliptree never shows the external ID to your customer; it's purely an internal hook.

What it's for

The main use is matching during import. When you re-import a customer CSV — for example, to update phone numbers in bulk — Sliptree uses the external ID to decide whether a row is an update to an existing customer or a new customer. Without an external ID, the matching falls back to the customer's name or email, which is less reliable when those change.

Set the external IDs once (either by hand or via your first import) and subsequent imports become idempotent: you can re-upload the same file repeatedly and end up with the same customers, just updated.

Where to set it

• In the UI — open a customer and edit the External ID field. Each external ID must be unique within your business.
• On import — include an ID column in your CSV. See Importing customers for the full column reference.
• From an export — exported customer CSVs include the external ID, making round-trips simple.

When you don't need one

If you never import customer data from elsewhere and you're managing customers entirely inside Sliptree, you can leave the external ID empty. It only earns its keep when you have another system as the source of truth.