Freight lines on orders are sent to Shopify with the following codes:
Amazon
Expedited: AMZEXP
FreeEconomy: AMZFRE
NextDay: AMZNXT
SameDay: AMZSMD
SecondDay: AMZSCD
Scheduled: AMZSCH
Standard: AMZSTD
Walmart
1-2 days: TwoDay
3-5 days: Standard
6-7 days: Value
6-10 days: Freight
eBay
E + 5-digit padded eBay Shipping Service ID.
e.g. E00010 for 'USPS First Class Package' Standard shipping on eBay.com
For the complete list of eBay shipping service IDs click here: