[BUG] Wrong error handling when 503 error message is received from ActiveCampaign API.

[elribonazo]

When activeCampaign load balancer returns a 503 error message. The NodeJS package is not able to parse or generate the response and returns the string "Error:", instead of "Error: ${error.message}" or something like that.

Expected behavior:

1. Returning the Error object
2. Return descriptive Error message for cases like those.

Current Behavior:

1. Returns an empty string as error
2. Try catch returns a string as an error, instead of an error object.