The tyre label is intended as an aid to support the user in an informed 'purchase' decision. It is crucial, therefore, that the user can see the label (and, if desired, the product information sheet) 'before' taking the purchase decision.
No obligation of displaying the label has been set for any document produced 'after' the payment or similar commitment by the customer. It is obviously a good practice to document the choice of the customer, once done, and for this a QR code or the human-readable equivalent URL could be printed in the invoice or analogous post-sales document, thus giving to the customer the possibility of having access to the full tyre registration in EPREL.
Disclaimer: Please note that the European Commission cannot provide a legally binding interpretation of the EU legislation, as this is the sole competence of the European Court of Justice. Any remarks from the European Commission services are without prejudice to the position the Commission might take should related cases arise in a procedure before the Court of Justice.