To inspect the full HTTP request you could send it to a URL provided by a service such as webhook.site @mbowler.
That said, your example data looks like you have two items:
Seeing you use an expression of Bearer {{$node["Get Agency Keys"].json["highLevelKey"]}} in your HTTP Request node, but you have only a single item on your highLevelKey node, what seems to happen here would be this: HTTP node misses the JSON payload for 2nd iteration - #2 by MutedJam
So, in addition to sending your data to webhook.site for debugging, you might also want to try out an expression such as Bearer {{ $("Get Agency Keys").first().json.highLevelKey }} to make sure you always use the first (and only) item from your Get Agency Keys node.