Apple ID is not valid

Get support and assistance from Apple directly, see  -> Contact Apple for help with Apple ID account security

Contact Apple for help with Apple ID account security - Apple Support

BTW:

You are sign in here .  .  .  with your Apple ID & Password.

Your Apple ID is the personal account you use with all Apple products and services. It includes the email address and password you use to sign in, as well as the contact, payment, and security details that you use with Apple.

You can’t merge multiple Apple ID accounts.

What happens when you use the same Apple ID & Password that you use to sign in here?

See the following Apple articles

Sign in with your Apple ID -> Sign in with your Apple ID - Apple Support

Manage and use your Apple ID -> Manage and use your Apple ID – Apple Support (UK)

Get support from Apple directly -> Get Support or call Apple in your region see -> Contact Apple for support and service or check -> here for more support and assistance.

Try the 2nd or 3rd blue link in my post.

If Apple Support cannot help you, that leaves you with your problem.

We are also users of Apple products & services like you.