I’m not sure how you are making your api requests (which tool or programming language), but the api key and username go in the http header.
Here is a curl example from the Discourse API Documentation
curl -X POST "http://127.0.0.1:3000/categories" \ -H "Content-Type: multipart/form-data;" \ -H "Api-Key: 714552c6148e1617aeab526d0606184b94a80ec048fc09894ff1a72b740c5f19" \ -H "Api-Username: discourse1" \ -F "name=89853c20-4409-e91a-a8ea-f6cdff96aaaa" \ -F "color=49d9e9" \ -F "text_color=f0fcfd"