In order to be approved to sell on Walmart.com, you will likely need to meet the following criteria:
Annual GMV (Gross Merchandise Volume) > $50K across all US marketplaces and ecommerce platforms
Have a US business entity and Tax ID
Not use FBA for Walmart orders, but can use other 3PL warehouses (Sellbrite integrates with 3PL service Deliverr for enabling 2-Day Shipping tags)
Only business function that can be outside the US is customer support (it has to be in English)
If you meet these criteria and would like to apply, you can do so here. Applications that come through Sellbrite are reviewed and approved faster than going direct to Walmart.com.