Hmm, just looking at this snippet, it looks like it is referring to the legacy key. The legacy key is the one located in Settings > Application and used with the xmlrpc api and typically points to https://yourapp.com/api/xmlrpc. If the request is going here, I suggest using the OAuth url below. OAuth on the other hand is a separate authentication from the legacy api key and you can still use the legacy api(xmlrpc) with OAuth.
For this problem in particular, I would need to see where the actual request is going to…
Here are the urls for each api when using OAuth, which we highly recommend.
xmlrpc: https://api.infusionsoft.com/crm/xmlrpc/v1
REST: https://api.infusionsoft.com/crm/rest/v1
Here are some helpful links to get started with OAuth as well as some of the jargon that can be thrown around in other posts among the community:
Glossary
Getting Started with OAuth