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Failing to connect to Lightsail Intance using Filezilla with SFTP

I have been trying to connect to my lightsail instance for days using sftp and the keyfile offered by aws lightsail in FileZilla. I have tried both new and default keys, but I keep getting the same error below.

Status:         Connecting to xx.xx.xxx.xx...
Status:         Using username "ubuntu". 
Status:         Server refused our key 
Error:          FATAL ERROR: No supported authentication methods available (server sent: publickey)
Error:          Could not connect to server
Status:         Waiting to retry...
Status:         Connecting to xx.xx.xxx.xx...
Response:   fzSftp started, protocol_version=11
Command:    keyfile "/Volumes/xxxxx/aws-xxxxxxx-certs-aahhrrgg/LightsailDefaultKey-eu-central-1.cer"
Command:    open "ubuntu@xx.xx.xxx.xx" 22
Status:         Using username "ubuntu". 
Status:         Server refused our key 
Error:          FATAL ERROR: No supported authentication methods available (server sent: publickey)
Error:          Could not connect to server
Error:          FATAL ERROR: Operation timed out