On labels downloaded after creating a Mondial Relay shipment, you can have the word “Specimen” where the barcode should be:

Mention specimen sur etiquette
Specimen mention on a label

This means that the plugin uses the Mondial Relay test account, as shown on this page of the documentation : https://mondialrelay-wp.com/doc/utiliser-le-mode-test/

To switch to production mode, you need to configure the “Account” tab of the plugin with your own Mondial Relay identifiers, as indicated in the dedicated page of the documentation : https://mondialrelay-wp.com/doc/connecter-le-plugin-a-votre-compte-mondial-relay/