The Download files endpoint supports projects with up to 10,000 key-language pairs. For instance, a project with 1,000 keys and 10 languages totals 10,000 key-language pairs.
For larger projects, use the Download files (Async) endpoint instead. Both endpoints share the same request payload, but the Async version returns a Process ID instead of a Download URL. You can then use the Retrieve a process endpoint to check the status and obtain the Download URL once the request is complete.