For using in app purchase ("IAP")，after do the set up at iTunes，the below set up is needed in Xcode.
What I did in the Xcode to access the product via IAP is listed as below.
0. Create the appropriate App ID to match the bundle ID in iTC, e.g. com.companyName.appName
1. Bundle Identifier: amend the content to match the bundle ID in iTC.
2. Code signing identity: install the appropriate provisional profile (for developer).
3. Product ID: assign the ID to match the product ID in iTC, e.g. com.companyName.appName.proName
4. Code signing identity: install the appropriate distribution provisional profile in Xcode.
MOST IMPORTANT: settle all the contract with APPLE in iTC. Otherwise, IAP never be enabled.