Step 2: Retrieve a presigned URL that can be used to upload a document (up to 5GB) to Liberty Mutual. The document will be associated with Submission Request Id returned from the POST Submission Request operation. This URL expires 15 minutes after its generation. Information on how to use the presigned URL can be found at https://stackoverflow.com/a/63915110. This step must be executed after the submission request data was sent to Liberty Mutual. Documents are uploaded one at a time, and after all documents are uploaded, the submission request will need to be submitted. Preferred approach for document upload that should be used whenever API consumers can support the use of presigned URLs.