After you are done with coding Mac OSX App you may want to upload the same to iTunes Connect to distribute it through Mac AppStore.
While validating your app archive before uploading it to iTunes Store you will get following error something like this stating: Archive validation failed due to the issue listed below. iTunes Store operation failed. App Sandbox not enabled. The following executable must include the “com.apple.security.app-sandbox” entitlement with a Boolean value of true in the entitlement property list.
Solution is Simple,
Step 01: Go to your Target in Xcode > Capabilities > slide App Sandbox toggle to right to make it on
Hope it helps,
Thanks & Regards