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Compatibility with FTP & FTPS

Because using FTP or FTPS (FTP over SSL) requires multiple dynamic ports for transferring data between server and client, ngrok is not a good solution for that traffic. We recommend using SFTP instead which relies on a single port number.

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ngrok with SFTP

You can use ngrok for SFTP communication by opening up a TCP endpoint on the port used by the SFTP server, usually port 22 (the same as SSH). 
ngrok tcp 22
TCP endpoints are only available on a free plan after adding a valid payment method to your account.
From there, you can use the resulting TCP address in your preferred SFTP client to connect to your local server.

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Alternatives to FTP for sharing files

If you’re just looking for a quick and easy way to serve local files, ngrok has a built in file server.