Most mobile browsers have issues downloading large files. In order to get the files onto your mobile device more easily, you can first download the file onto your desktop and then transfer the file using the below instructions.
Transferring files to iPhone/iPad from Mac
eBook files (e.g. EPUBs) should automatically be added to your Apple Books library
You can then follow these instructions to sync your Mac Books library with your iPhone/iPad: Sync books between your Mac and iPhone or iPad
Transferring files to Android from PC
1. Make sure that your device’s screen is unlocked.
2. Connect your device to your computer using a USB cable. If you’re asked to select a USB connection on your device, choose Media device (MTP).
3. Use the File Transfer window that pops up on your computer to drag and drop files, just like other external devices.
Transferring files to Android from Mac
1. Android File Transfer is an application for Macintosh computers (running Mac OS X 10.5 or later) you can use to view and transfer files between your Mac and an Android device (running Android 3.0 or later). Download here.
2. When the download completes, double-click androidfiletransfer.dmg and in the Installer window, drag Android File Transfer to Applications.
3. Use the USB cable that came with your Android device to connect it to your Mac.
4. Double-click Android File Transfer to open it the first time (subsequently, it opens automatically).
5. Browse the files and folders on your Android device, add folders, copy files up to 4GB to or from your Mac onto your Android device.