You need to share following details to investigate the issue:
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Admin URL of the concerned site with login credentials.
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SFTP/FTP Details such as Host Name, Port, Username, Password.
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Salesforce login credentials. Or, you may grant login access for Salesforce as well: How to Grant Login Access
NOTE: Mandatory to share SFTP/FTP details and all of the concerned site such as Host Name, Port, User, and Password if we require while investigation. You may create a Development site (complete replica of the Live site) and share all above-mentioned detail to debug the issue.