During the connection to Oracle 12.2 databases, this error is occurring due to the older client version of the client and the connection cannot be established. If the client version of the client can be upgraded, the problem will be solved. But since there are many different clients, you can follow these steps for a permanent solution.
Add the following lines to the sqlnet.ora file under the current TNS_ADMIN directory for the grid and database home. If this file is not present on the database side, it needs to be created.
The TNS_ADMIN directory is generally as follows.
Then restart the database instances or database.
srvctl stop database -d ORCL
srvctl start database -d ORCL