What do I do when it won’t let me sign into Apple ID

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?

Check your Apple ID via your email box, see this Apple article: If you forgot your Apple ID

If you forgot your Apple ID email address or phone number - Apple Support                  

OR see -> Having trouble signing in?

https://iforgot.apple.com/password/verify/appleid

See -> If you can't connect or sign in to iCloud

If you can't connect or sign in to iCloud - Apple Support

See this Apple article: If you forgot your Apple ID password

If you forgot your Apple ID password - Apple Support

Then see this Apple article: What to do after you change your Apple ID or password

What to do after you change your Apple ID or password - Apple Support

Or do you need your Passcode to unlock the iPhone?

If so, see -. How to reset your iPhone, iPad or iPod touch if you've forgotten your passcode

How to remove your iPhone, iPad or iPod touch passcode without a computer – Apple Support (UK)