Step 1 : Go to iTunes Connect and login to your Apple Developer account
Step 2 : Click on My Apps
Step 3 : Click on the app or click on + to add new app
Step 4 : Click on Manage under In-app Purchases present on left hand side panel
Step 5 : Click on + to add In-app Purchases
Step 6 : A popup will open, select the type of In-App Purchases you want
Step 7 : Click on Create
Step 8 : Enter all the necessary details, such as Reference Name, Product ID, Price, Display Name, and Description
Step 9 : Click on Save
Step 10 : Here is your Product ID(Package ID), copy it. Go to In-App Purchases
Please note : You need to follow the same steps from step 5 to step 10 to generate weekly , monthly and yearly subscription package ID
Step 11 : Click on App-Specific Shared Secret option
Step 12 : Click on Generate App-Specific Shared Secret
Step 13 : Here is your Shared Secret key, copy it and click on Done
Step 14 : Now paste the copied keys in their respective fields on creator software