Streaming from iPad to Apple TV

Thank you for that information.

You should be able to access Apple TV+ directly on the Apple TV box, without needing AirPlay from an iPad.

You should be able to AirPlay with audio from beginning to end, although Apple TV+ end credits for dubbing are silent by design.

If the issue persist, then consider contacting the Apple Support staff. Contact Apple for support and service - Apple Support

What is your model Apple TV box? Identify your Apple TV model - Apple Support

unable to complete the sign in.

If you have an Apple TV (2nd or 3rd generation) and two-factor authentication for your Apple ID, then you may be asked to type your password followed by the six-digit verification code directly into the password field. Additionally, there is a time limit, after which the code becomes invalid.

Try this: First enter the characters of your password (do not submit yet), then manually request a new verification code, then append that code to the password (no spaces or other separating characters), and then submit. That should help you get passed the time limit.