Do you think developers know what your actual product or service does for what they are using the API for? Your product or service may need specific knowledge. Like accounting software, payment service or transcription service. If you don’t understand how that works, it’s hardly possible to understand what the API does.
You might be tempted to put flow charts or sequence diagrams in your API documentation. This usually happens, if someone has done diagrams while developing the API. Because a picture tells more than a thousand words, right?
Those diagrams that are often drawn from internal perspective. And they are missing the user flow of your product. If you have 10 different endpoints for your API, the external developer will most likely need a process diagram. It should show typical flow to use your product or accomplish a specific task in the product. As a bonus also what endpoints are needed. Clarify this in 1-5 simple bullet points as a list. If you can’t, then maybe consider simplifying the actual product?