Most marketplaces allow you to have your orders sent off to Amazon to be filled by their fulfillment centers. This is an extremely handy feature that Listing Mirror has, and can be very helpful to your business if you don't want to manage a warehouse but want to expand to non-Amazon marketplaces.
Walmart, however, does not allow Amazon to fill their orders. It is strictly against their policy, and if discovered that you are filling your Walmart orders with FBA, you could be suspended or in some cases banned from the marketplace entirely.
Listing Mirror will not stop you from setting up your Walmart marketplace to work with FBA, but you will need to reach out to Listing Mirror support to enable any kind of automation for MCF for your Walmart integrations.
Amazon has unique tracking numbers that begin with TBA, so Walmart will be able to tell if you're shipping items from Amazon, even if you think they won't.
Listing Mirror offers integrations to FBA alternatives, like Deliverr and RSL(Rakuten), if you would like to work with Walmart but you don't want to manage a warehouse, one of those fulfillment options are safe for Walmart and don't put your account at risk. Furthermore they can both be used to fill orders on other channels as well, so you won't have to have the inventory source for Walmart alone!
If you have any questions about 3PLs that can help your business, please reach out to our support!