Kindly note that you have not given me any information about your Akeeba Backup version, PHP version, Kickstart version, and WordPress version. You have not given me any information about whether you have a multipart backup archive or not. Moreover, you have given me no information about how these files were downloaded and uploaded. Moreover, you have not indicated that you followed any of the instructions included for your convenience in the error message itself. Therefore, I have to repeat the same information.
Do you have a multipart backup archive? Note that the Manage Backups page does tell you when you click the info icon next to a backup record. If this is the case, your backup archive consists of multiple files (files with the same name and extensions `.jpa`, `.j01`, `.j02`, etc). Some of those files are missing, corrupt, or truncated. You will need all of these files to be present in the same directory.
Please make sure to download and upload all of your backup archive files using either SFTP or FTP in Binary transfer mode. Any other way, including downloading through the web interface or your hosting control panel's file manager, may lead to corrupt backup archives. Moreover, do check that their file size matches the sizes reported in the Manage Backups page of Akeeba Backup. Perform this check both when downloading the files, and when uploading them to the server you are restoring your backup into.
Your backup archive may also have got corrupt if you had a large file at backup time which changed size while being backed up, breaking the backup. This issue has been addressed since Akeeba Backup for WordPress 9.0.3.
Nicholas K. Dionysopoulos
Lead Developer and Director
🇬🇷Greek: native 🇬🇧English: excellent 🇫🇷French: basic • 🕐 My time zone is Europe / Athens
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