If you have carefully followed this guide to create an Apple Business Manager Account: https://support.iris.net/en/support/solutions/articles/24000054884-set-up-an-apple-business-manager-account-to-distribute-iris-apps and do not have an MDM to distribute your App, you can use Redemption Codes.
>in Apple Business Manager : https://business.apple.com, please navigate to Custom Apps:
Select the App > on License Type select Redemption Code > Assign a Quantity of Licenses you want to deploy:
You will be able to download an csv file with a list of Redemption code that you can share to end users:
A redemption code should be linked to an Apple Id, so you will need as many Licenses as Apple Ids. Please Follow this Process to install iOS Apps via Redeem codes on an iPad.