You may receive the following error while connecting the FTP.
421 Too many connections (10) from this IP
You will receive this error if your FTP client is reached to maximum connection limit.
Please refer to the following steps to configure the Maximum number of connections in FileZilla to fix this issue.
1. Open FileZilla.
2. Go to Files >> Site Manager.
3. Click on the Transfer Settings tab.
4. Untick the Limit number of simultaneous connections or configure the Maximum number of connections. (more than 10 and less than your server limit)
5. Click the OK Button and connect again.