[url=https://www.phpbb.com/support/docs/en/3.3/kb/article/transferring-your-board-to-a-new-host-or-domain/]Knowledge Base - Transferring Your Board to a New Host or Domain[/url]

In Section Restore - Restoring the Database - 2) If the database file is greater than 2MB (exactly) and you wish to use BigDump, follow these instructions

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With FileZilla, open an FTP connection to your server. Create a new directory somewhere on your server and name it dump. Set the permissions of this folder to full write. Most often, you will need to right click the file and select File permissions or Properties. Set the permissions to 777, as shown below.