Permission denied (publickey) when connecting to ubuntu server using SSH


I was able to connect to the server using SSH but somehow i am getting permission denied (publickey), I am sure this is a duplicate question but none of the answer is able to solve the problem for me. I will appreciate if anyone able to help me with this issue.

Provided solutions for the similar question on askubuntu is not helpful enough to solve this problem

ssh -p PORT_NUMBER -i devops.pem ubuntu@MACHING_IP

OpenSSH_7.9p1, LibreSSL 2.7.3 debug1: Reading configuration data /etc/ssh/ssh_config debug1: /etc/ssh/ssh_config line 48: Applying options for * debug2: resolve_canonicalize: hostname machine_ip is address debug2: ssh_connect_direct debug1: Connecting to machine_ip [machine_ip] port 323. debug1: Connection established. debug1: identity file devops.pem type -1 debug1: identity file devops.pem-cert type -1 debug1: Local version string SSH-2.0-OpenSSH_7.9 debug1: Remote protocol version 2.0, remote software version  OpenSSH_6.6.1p1 Ubuntu-2ubuntu2.13 debug1: match: OpenSSH_6.6.1p1 Ubuntu-2ubuntu2.13 pat OpenSSH_6.6.1* compat 0x04000002 debug2: fd 3 setting O_NONBLOCK debug1: Authenticating to machine_ip:323 as 'ubuntu' debug3: put_host_port: [machine_ip]:323 debug3: hostkeys_foreach: reading file  "/Users/myname/.ssh/known_hosts" debug3: record_hostkey: found key type ECDSA in file  /Users/myname/.ssh/known_hosts:16 debug3: load_hostkeys: loaded 1 keys from [3.83.164.43]:323 debug3: order_hostkeyalgs: prefer hostkeyalgs: ecdsa-sha2-nistp256-  cert-v01@openssh.com,ecdsa-sha2-nistp384-cert-v01@openssh.com,ecdsa-sha2-nistp521-cert-v01@openssh.com,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521 debug3: send packet: type 20 debug1: SSH2_MSG_KEXINIT sent debug3: receive packet: type 20 debug1: SSH2_MSG_KEXINIT received debug2: local client KEXINIT proposal debug2: KEX algorithms: curve25519-sha256,curve25519-  sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group14-sha256,diffie-hellman-group14-sha1,ext-info-c debug2: host key algorithms: ecdsa-sha2-nistp256-cert-v01@openssh.com,ecdsa-sha2-nistp384-cert-v01@openssh.com,ecdsa-sha2-nistp521-cert-v01@openssh.com,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,ssh-ed25519-cert-v01@openssh.com,rsa-sha2-512-  cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,ssh-rsa-cert-v01@openssh.com,ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa debug2: ciphers ctos: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com debug2: ciphers stoc: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com debug2: MACs ctos: umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1 debug2: MACs stoc: umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1 debug2: compression ctos: none,zlib@openssh.com,zlib debug2: compression stoc: none,zlib@openssh.com,zlib debug2: languages ctos:  debug2: languages stoc:  debug2: first_kex_follows 0  debug2: reserved 0  debug2: peer server KEXINIT proposal debug2: KEX algorithms: curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1 debug2: host key algorithms: ssh-rsa,ssh-dss,ecdsa-sha2-nistp256,ssh-ed25519 debug2: ciphers ctos: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-gcm@openssh.com,aes256-gcm@openssh.com,chacha20-poly1305@openssh.com,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,rijndael-cbc@lysator.liu.se debug2: ciphers stoc: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-gcm@openssh.com,aes256-gcm@openssh.com,chacha20-poly1305@openssh.com,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,rijndael-cbc@lysator.liu.se debug2: MACs ctos: hmac-md5-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-ripemd160-etm@openssh.com,hmac-sha1-96-etm@openssh.com,hmac-md5-96-etm@openssh.com,hmac-md5,hmac-sha1,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96  debug2: MACs stoc: hmac-md5-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-ripemd160-etm@openssh.com,hmac-sha1-96-etm@openssh.com,hmac-md5-96-etm@openssh.com,hmac-md5,hmac-sha1,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96  debug2: compression ctos: none,zlib@openssh.com  debug2: compression stoc: none,zlib@openssh.com  debug2: languages ctos:   debug2: languages stoc:   debug2: first_kex_follows 0   debug2: reserved 0   debug1: kex: algorithm: curve25519-sha256@libssh.org  debug1: kex: host key algorithm: ecdsa-sha2-nistp256  debug1: kex: server->client cipher: chacha20-poly1305@openssh.com MAC:   <implicit> compression: none  debug1: kex: client->server cipher: chacha20-poly1305@openssh.com MAC:   <implicit> compression: none  debug3: send packet: type 30  debug1: expecting SSH2_MSG_KEX_ECDH_REPLY  debug3: receive packet: type 31  debug1: Server host key: ecdsa-sha2-nistp256   SHA256:iKUGAwvNeyafz8bT6N2ljbs5dES2cLF7WbmJ9mGvHgY  debug3: put_host_port: [machine_ip]:323  debug3: put_host_port: [machine_ip]:323  debug3: hostkeys_foreach: reading file   "/Users/myname/.ssh/known_hosts"  debug3: record_hostkey: found key type ECDSA in file   /Users/myname/.ssh/known_hosts:16  debug3: load_hostkeys: loaded 1 keys from [machine_ip]:323  debug3: hostkeys_foreach: reading file   "/Users/myname/.ssh/known_hosts"  debug3: record_hostkey: found key type ECDSA in file   /Users/myname/.ssh/known_hosts:16  debug3: load_hostkeys: loaded 1 keys from [machine_ip]:323  debug1: Host '[machine_ip]:323' is known and matches the ECDSA host key.  debug1: Found key in /Users/myname/.ssh/known_hosts:16  debug3: send packet: type 21  debug2: set_newkeys: mode 1  debug1: rekey after 134217728 blocks  debug1: SSH2_MSG_NEWKEYS sent  debug1: expecting SSH2_MSG_NEWKEYS  debug3: receive packet: type 21  debug1: SSH2_MSG_NEWKEYS received  debug2: set_newkeys: mode 0  debug1: rekey after 134217728 blocks  debug1: Will attempt key: devops.pem  explicit  debug2: pubkey_prepare: done  debug3: send packet: type 5  debug3: receive packet: type 6  debug2: service_accept: ssh-userauth  debug1: SSH2_MSG_SERVICE_ACCEPT received  debug3: send packet: type 50  debug3: receive packet: type 51  debug1: Authentications that can continue: publickey  debug3: start over, passed a different list publickey  debug3: preferred publickey,keyboard-interactive,password  debug3: authmethod_lookup publickey  debug3: remaining preferred: keyboard-interactive,password  debug3: authmethod_is_enabled publickey  debug1: Next authentication method: publickey  debug1: Trying private key: devops.pem  debug3: sign_and_send_pubkey: RSA   SHA256:i7X0CUB2OrfNpQLcWo2e6/L7Td3uGixA2xKAzU8CiI8  debug3: sign_and_send_pubkey: signing using ssh-rsa  debug3: send packet: type 50  debug2: we sent a publickey packet, wait for reply  debug3: receive packet: type 51  debug1: Authentications that can continue: publickey  debug2: we did not send a packet, disable method  debug1: No more authentication methods to try.  ubuntu@machine_ip: Permission denied (publickey).