master to minion communication issues while running salt state.apply

[Subit Ku. Das]

  The salt master version is 3002.6

The salt minion version is 3002.9

Salt key is getting generated successfully in master. But while running salt state.apply

, I am getting the below error.

[DEBUG   ] Trying to connect to: tcp://XX.XX.XX.XX:4506

[DEBUG   ] salt.crypt.get_rsa_pub_key: Loading public key

[ERROR   ] Sign-in attempt failed: {'enc': 'pub', 'pub_key': '-----BEGIN PUBLIC KEY-----\n<public key>\n-----END PUBLIC KEY-----\n', 'publish_port': 4505, 'aes':[DEBUG   ] Closing AsyncZeroMQReqChannel instance

I checked the network as well as firewall. I checked as per the link below.
Troubleshooting the Salt Minion (saltproject.io)
 Everything is fine from servers' end. Direct ssh between the salt and the master is also working. 

As per a suggestion in the below forum, the master has to be higher in version than minions and should be upgraded before minions.
After upgrading minions to 3004.1+ds-1 they fail to connect to a master running 3004+ds-1 · Issue #61867 · saltstack/salt (github.com)

Is that the only reason for such errors?
Do I need to check something else other that version upgrade ?
Because, as I have mentioned earlier salt master and minion versions are same, but minor version of minion is higher than master.  (master 3002.6, minion 3002.9)

The salt master is running in RHEL7 whereas salt minion is running in RHEL8.