Codesign tutorial - step by step (I can get it to work)

Trying to upload an ipa to the app store and it said it wasn't signed.

The exact vague error is:

Application failed codesign verification. The signature was invalid, contains disallowed entitlements, or it was not signed with an iPhone Distribution Certificate.

So the signature should be valid as I just remade the certificate and PP. Not sure what a disallowed entitlement is. It was signed with an iPhone Distribution Certificate.

Do I need to run codesign on it? How do I get to the app and what do I type in Terminal to get it verified?

I am on the edge of giving up making apps for Apple altogether. It literally takes longer to upload it than to make some of them.

Thanks.