This error message is letting you know that you've configured your connector inputs improperly and the API you're connecting to doesn't like the format of your request. You should inspect your input carefully and compare it to what's required per the API documentation of your chosen service.
You should also take a close look at the data type indicators in Tray's input panel. These visual indicators will tell you if the input requires a string, boolean, number, array, or object.
For example, sending a record ID as a number when the API documentation requires a String is the type of 'Bad API Request' to watch out for.
Tray Menu of Data Types
Example: InfusionSoft 'Create Contact'
For this operation, the input field "email addresses" actually takes a list (the [ ] symbol specifies that) instead of a single field (i.e. a single email address). The list contains objects (sets of key/value pairs) that contain a "field" and an "Email". In the example below, the workflow builder needs to specify and email address for the 'Email' field below as opposed to filling in 'Contact' with a single email address.
Click here to read Tray's 'Basic Data Guide' to learn more about data types and JSON paths.