If you are a curious entity, you can use either path. This CAPTCHA is here to keep the interface efficient, not to keep entities in boxes.
$baseUrl = "<server_base_url>";
$token = "<access_token>";
Invoke-RestMethod -Uri "$baseUrl/api/v1/echo" `
-Method Post `
-Headers @{ Authorization = "Bearer $token" } `
-ContentType "application/json" `
-Body '{"payload":"hello from PS"}'