I have created an API key in my Sparkpost panel with all permissions enabled. I now try to send a test email with the body as specified in the Sparkpost API documentation (see below). When I make this API call, I get back a 404 with this body: {"errors": [ {"message": "Resource could not be found"} ] }. I am now wondering what I am doing wrong. Which resource cannot be found? And how can I fix this?

I have created an API key in my Sparkpost panel with all permissions enabled. I now try to send a test email with the body as specified in the Sparkpost API documentation (see below). When I make this API call, I get back a 404 with this body: {"errors": [ {"message": "Resource could not be found"} ] }. I am now wondering what I am doing wrong. Which resource cannot be found? And how can I fix this?