Have I Been Pwned?

If they are all from the same domain, and you have ownership of the domain, you can use Domain Search.

Otherwise, you can feed them into the API one-by-one, with curl, python requests, or likewise: GET https://haveibeenpwned.com/api/v2/breachedaccount/{account}

The API is rate-limited to 1 request every 1.5 seconds, so it may take awhile, depending on the size of your list.

Here's the answer from the CTI Vendor. (Name replaced with Vendor X)

For HIBP, Vendor X had a custom and paid integration. Vendor X paid HIBP a fee whenever a new breach (which Vendor X did not have) was acquired by HIBP. Therefore, we did not use the Open API, we built a custom integration that pushed any new breach acquired by HIBP into the Vendor X portal. This was the reason no passwords were ever present in HIBP breaches in Vendor's portal (paid service), because under UK and GDPR law, any exchange of PII (including passwords) between any two entities, where money is involved, is a crime.

What’s the breach it said it was named in? Should give you a description.

It’s from when a company got hacked and grabbed the data. Usually never at fault of your own, change the password you used from that data breach on any account that uses that password, and never use it again

You have to assume some hacker has a giant list of passwords with that on there and will try to login on any site possible

In Cybersecurity, paranoia is your friend.