How do redemption codes work in Apple Business Manager when NOT using MDM
I am also using Apple Business Manager for my company but we have an MDM also with it. However, on your question, I think you have to go through the following steps:


Log in to your Apple Developer Account connect your App to the client’s Apple Business Manager account by adding their Organization ID and Company Name for distribution. See the highlighted blue area below.





This connection is immediate. Once your App is connected to the client’s Apple Business Manager Account, it will be visible under the Custom App section of the ABM account.
By selecting that custom app, you can generate 1-time use redemption codes and links for employees to download your app.




Once the codes are created, you can download the list.



You can use these codes and proprietary processes to enable your client’s employees to access your application.