Pardot: Form data not submitted to Pardot due to expired API key

Description

In Pardot, the API Key is valid for 60 minutes, after which a new key is generated. This procedure works fine for other API calls, like retrieving prospect fields and prospect data. But when saving a prospect, the outdated key was being used. This caused a failure in the API call with the error message: "Either the user and/or API keys are incorrect, or the API key has expired."