What is the difference between a client ID and an API key?

I’m using the PHP SDK from this address: GitHub - infusionsoft/infusionsoft-php: PHP client library for the Infusionsoft API.

And I’ve been given, by the Infusionsoft account owner, an API key and host (I don’t have direct access to their account, I’m just sending data to it):

Host = xy123.infusionsoft.com
API Key = 4f9f09cbd48cddaae6907bb50445650e

I’ve changed them a bit for privacy reason but it’s basically a domain name and 32 characters hex string. They insist it’s all I need to use the API, however the SDK refers to a client ID and secret which have a completely different format (just to be sure, I’ve tried with the information they’ve provided and it didn’t work).

So I’m wondering, is it possible to connect to the API via the SDK using this host and API key? And if so how can I do this?

the way to use the api key with the sdk would be to instantiate the iSDK object (say you call it $app) and then call

$app=cfgCon(‘ab123’,‘api key here’);