To create bulk discount codes for the app, you will need to use a bulk discount code generator apps. One such app is https://apps.shopify.com/bulk-discount-generator

Step 1 - Install the app on your Shopify store.

Step 2 - Once installed, open the app on your Shopify Admin.

Step 3 - Click on Create discount set.

Step 4 - Give it a name and you can complete the configuration. To make it app only, click on advanced settings and add a suffix to it.

Get the suffix for your store.

Step 5 - Configure the offer type and discount usage

Step 6 - Click on Save. It will take few minutes to generate the codes

Step 7 - Once generated you can click on export codes and download the CSV

PLEASE SHARE THE CODES TO CUSTOMERS WITHOUT THE SUFFIX USED.

FOR EXAMPLE -

Code generated: G2YR2G-APPONLY

Code to be shared to customer/or to be used on app: G2YR2G (Without suffix)

Suffix is just for backend reference, not for customer view.