Miravia API Connection Assistance

I'm currently experiencing issues connecting to the Miravia API using Java. I have the API Key and have followed the documentation, but I'm receiving an 'Invalid API Key' error. I'm not quite sure how to check if my API key needs to be in a specific format or if it's encoded incorrectly.

Your assistance is required to:
- Help me authenticate correctly
- Guide me on how to format and check the API key
- Assist me in making a simple request (GET or POST) to test the connection

Ideal skills for this job include:
- Extensive experience with Java
- Proven track record of integrating APIs
- Strong troubleshooting skills
- Ability to explain technical concepts clearly