The Walmart SKU Override error means the Product Identifier you are using for the Walmart SKU already exists in your Walmart account but under a different SKU.
Listing Mirror will automatically tell Walmart to change the listing's existing SKU to match what is in Listing Mirror. More often than not, these types of errors resolve themselves within a day or two.
If the event the error does not resolve itself:
1. Go to Walmart Seller Center and search for the listing's Product Identifier.
2. Change the SKU to match the SKU in Listing Mirror.
☎️ If you're still not able to resolve the issue, contact Listing Mirror Support to request the FEED ID# (be sure to include the SKU as well).
Next, use the FEED ID# to open a case with the Walmart support team so they can correct the issue on their end.