Credibility of Invoice from Walmart

I have online purchased an AirPods Pro from Walmart, US. The receipt provided by them has only an Order number and a Barcode. There is no serial number associated with it. I checked with Walmart and it seems like they don’t tag the serial number in their invoice. Now I am in India, trying to service them but getting denied because of the serial number not included in the invoice. The iCare service center nor the Apple customer care support from India have no idea and are denying the credibility of the invoice.

Is Walmart’s invoice of Apple products not a valid one and internationally recognised?

What should be done to get my AirPods fixed?

Please provide your inputs