Figured out I had to Base64 encode the API Key.
This worked so far with some limitations:
let
Source = Json.Document(Web.Contents("https://api.insight.ly/v2.2/Contacts", [Headers=[Authorization="Basic ***********", ContentType="application/json"]])),
#"Converted to Table" = Table.FromList(Source, Splitter.SplitByNothing(), null, null, ExtraValues.Error),
#"Expanded {0}" = Table.ExpandRecordColumn(#"Converted to Table", "Column1", {"CONTACT_ID", "SALUTATION", "FIRST_NAME", "LAST_NAME", "BACKGROUND", "IMAGE_URL", "DEFAULT_LINKED_ORGANISATION", "OWNER_USER_ID", "DATE_CREATED_UTC", "DATE_UPDATED_UTC", "VISIBLE_TO", "VISIBLE_TEAM_ID", "VISIBLE_USER_IDS", "CUSTOMFIELDS", "ADDRESSES", "CONTACTINFOS", "DATES", "TAGS", "LINKS", "CONTACTLINKS", "CAN_EDIT", "CAN_DELETE", "SOCIAL_LINKEDIN", "SOCIAL_FACEBOOK", "SOCIAL_TWITTER", "ASSISTANT_NAME"}, {"CONTACT_ID", "SALUTATION", "FIRST_NAME", "LAST_NAME", "BACKGROUND", "IMAGE_URL", "DEFAULT_LINKED_ORGANISATION", "OWNER_USER_ID", "DATE_CREATED_UTC", "DATE_UPDATED_UTC", "VISIBLE_TO", "VISIBLE_TEAM_ID", "VISIBLE_USER_IDS", "CUSTOMFIELDS", "ADDRESSES", "CONTACTINFOS", "DATES", "TAGS", "LINKS", "CONTACTLINKS", "CAN_EDIT", "CAN_DELETE", "SOCIAL_LINKEDIN", "SOCIAL_FACEBOOK", "SOCIAL_TWITTER", "ASSISTANT_NAME"})
in
#"Expanded {0}"
