Thanks for the screenshots. They show what’s going on. You’re trying to add a custom model named gpt-5.5, but that name is already taken by a built-in Cursor model GPT-5.5. Because of the name conflict, the Add Custom Model button doesn’t create anything, and requests still go through Cursor’s native routing instead of BYOK.
Fix: give your model a unique name that’s different from the built-in ones. For example, use gpt-5.5-relay (or any name that isn’t in Cursor’s list) and click Add Custom Model. It should then appear in the list and route through your Base URL and key.
Your Base URL and API Key are set up correctly, so you don’t need to change anything there.
This was also discussed here if it helps: Routing ambiguity when custom model name matches a built-in Cursor model
Let me know how it goes.