Your domain is registered with vercel?

Yes

I’ve copy the auth code and then what will I do next?

You want to transfer to some other provider?

if its to another vercel account, I don't think auth code is required

Do I need to have a Vercel Pro plan to do this?

I don't think you need

There is nowhere mentioned on the docs, so I don't think you need

And Also:

Due to ICANN rules, a domain must be registered with a registrar for 60 days before it can be transferred to another.

if your domain was registered anywhere in the past 60 days, you can't transfer now

Edit: its only for transferring to other registrars

Actually I’ve brought a domain on Vercel and now I’ve to leave the project to someone else trying to send the domain to his organization so he can use it

Yes it has actually 117days

This should help I think

I’ve done this before?

As you can see I have this one that I want to transfert to someone else Vercel account

Thé transfert out only generate an auth code. And when trying to transfert in adding the domaine name and the auth code getting an error

I think they would need to add you to their team

Its best to contact vercel support for it now

Nothing is mentioned in vercel docs about this, so you'll have to contact support only for it

I’m getting this error.

.