The walmart integration does not set values for email, customer ID, or payment method. While those fields are not necessary to ship the order, we pull all shipments out of shipstation via the API to import into our financial system of record (Netsuite).
If no customer ID is provided by walmart, use the internal shipstation customer ID so it's not null.
If no payment method is supplied by walmart, hardcode something like 'walmart'.
Email address would be nice to ask walmart to provide. Ebay and Amazon provide it.