Did some search and maybe reading about the topic in general could help:
- https://softwareengineering.stackexchange.com/questions/353145/where-to-place-an-api-key-a-custom-http-header-vs-the-authorization-header-with
- https://stackoverflow.com/questions/5517281/place-api-key-in-headers-or-url
- https://tools.ietf.org/html/rfc7235
You can have it as part of the request, in the header under different tags (not an expert here). In your case, you don’t get to choose where to send it but it will be your API the one that dictates how to use it. Check the documentation, hunt for examples or even sent a short email to the API owners and they could assist you, specially if it is not clear in their documentation. Good luck,
Kf