## MedicationOrderExtensions.messageIdSystem property [​](/content/docs/sdk/core.medicationorderextensions.messageidsystem#medicationorderextensionsmessageidsystem-property/index.html)

Identifier system for the vendor's per-prescription message id (SureScripts `messageId` in ScriptSure). Stamped on a draft `MedicationRequest` by the cart-checkout flow and used to reconcile the approval webhook back to the draft. Optional so existing single-order consumers don't have to populate it. Consumed by the paired `medplum-ee` cart-checkout / prescription-webhook bots.

**Signature:**

```typescript
readonly messageIdSystem?: string;
```

- [MedicationOrderExtensions.messageIdSystem property](/content/docs/sdk/core/medicationorderextensions.messageidsystem#medicationorderextensionsmessageidsystem-property/index.html)