Google App script to fill the cells of a column in a sheet with a string retrieved from a http GET call

Create a Google App script for sheets, to fill the cells of a column with a string retrieved from a REST http GET API. The API call needs to have a custom header added, containing an access key. When the retrieved text length is bigger than 50000 (max length of a google sheet size), mark the cell with a red background color. The google sheet, API url and access key will be provided upon agreement.