I'm buying Apple Care Plus, but there's an error, so why is that?

I'd like to purchase Apple Care Plus, but I see an error as below. Why is that?

We're Sorry

You've reached the code limit and we're unable to complete your request. Please try again later.

Return to Apple Support site.

456 2018-11-05 Gentleman

He's got a code limit, so he wants me to try it later
Try it later

Gentleman 7 years ago 0

Yes, I understand English but I don't know what code limit is...

Gentleman 7 years ago 0

I'll do it in a few hours
I had the same problem, but it worked after I waited

Gentleman 7 years ago 0

I'll have to wait a few hours

Gentleman 7 years ago 0

Not a few hours, but an hour later

Gentleman 7 years ago 0

If you check your serial number several times, that's what I know
Try it later, as it says above

Gentleman 7 years ago 0

I see. Thank you for the information
I succeeded now!

Gentleman 7 years ago 0