The following method is not listed in the On-Prem swagger page but I did find it when searching the support site, however it returns a 404 (Does not exist) from my On-Prem installation. Does it only exist in the Cloud API?
repository/v1/Repositories/<Repository Name>/Entries/<Folder ID>/<Document Name>
https://developer.laserfiche.com/guides/guide_importing-documents.html