Actually, there is always confusing between where to set the database name, Tns name in the dataguard parameter which parameter used what to specify the configuration of parameter in configuring the dataguard environment in oracle.

Which parameter use TNS names and DB name?

Following table give the use of parameter:

Uses	Parameters
DB_NAME	DB_NAME
DB_UNIQUE_NAME	DB_UNIQUE_NAME, LOG_ARCHIVE_CONFIG
TNS Service Name	LOG_ARCHIVE_DEST_2, FAL_SERVER
None (Path/Format)	CONTROL_FILES, LOG_ARCHIVE_DEST_1, REMOTE_LOGIN_PASSWORDFILE, LOG_ARCHIVE_FORMAT, DB_FILE_NAME_CONVERT, LOG_FILE_NAME_CONVERT, STANDBY_FILE_MANAGEMENT

Consider the following entry for more clarity:

Role	DB_UNIQUE_NAME	TNS Service Name
Primary Database	chicagodb	chicagotns
Standby Database	bostondb	bostontns

Parameter used in database:

DB_NAME=chicago
DB_UNIQUE_NAME=chicagodb

LOG_ARCHIVE_CONFIG='DG_CONFIG=(chicagodb,bostondb)'

CONTROL_FILES='/arch1/chicago/control1.ctl', '/arch2/chicago/control2.ctl'

LOG_ARCHIVE_DEST_1=
 'LOCATION=USE_DB_RECOVERY_FILE_DEST 
  VALID_FOR=(ALL_LOGFILES,ALL_ROLES)
  DB_UNIQUE_NAME=chicagodb'

LOG_ARCHIVE_DEST_2=
 'SERVICE=bostontns ASYNC
  VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE) 
  DB_UNIQUE_NAME=bostondb'

REMOTE_LOGIN_PASSWORDFILE=EXCLUSIVE

LOG_ARCHIVE_FORMAT=%t_%s_%r.arc

Overview of parameter used in Oracle Dataguard:

Parameter	Purpose	Uses	Example / Notes
DB_NAME	Name of the database as created originally.	✅ DB_NAME	Same on primary and standby. E.g., DB_NAME=chicago
DB_UNIQUE_NAME	Unique identifier for each database in the configuration.	✅ DB_UNIQUE_NAME	E.g., DB_UNIQUE_NAME=chicago, DB_UNIQUE_NAME=boston
LOG_ARCHIVE_CONFIG	Enables Data Guard and lists all participating databases.	✅ DB_UNIQUE_NAME	E.g., LOG_ARCHIVE_CONFIG='DG_CONFIG=(chicago,boston)'
CONTROL_FILES	Path to control files for database recovery.	❌ None	E.g., CONTROL_FILES='/oradata/control01.ctl','/oradata/control02.ctl'
LOG_ARCHIVE_DEST_1	Local archive destination for redo logs.	❌ None	E.g., LOCATION=/arch1/chicago/
LOG_ARCHIVE_DEST_2	Remote destination for redo logs (standby).	✅ TNS Service Name	E.g., SERVICE=boston (TNS entry for standby)
REMOTE_LOGIN_PASSWORDFILE	Enables remote authentication for redo transport.	❌ None	Set to EXCLUSIVE or SHARED
LOG_ARCHIVE_FORMAT	Format for archived redo log filenames.	❌ None	E.g., LOG_ARCHIVE_FORMAT=log_%t_%s_%r.arc
FAL_SERVER	TNS name of the primary database used by standby to fetch missing logs.	✅ TNS Service Name	E.g., FAL_SERVER=boston (TNS entry of primary)
DB_FILE_NAME_CONVERT	Converts primary data file paths to standby paths.	❌ None	E.g., ('/oradata/chicago/','/oradata/boston/')
LOG_FILE_NAME_CONVERT	Converts primary redo log file paths to standby paths.	❌ None	E.g., ('/log/chicago/','/log/boston/')
STANDBY_FILE_MANAGEMENT	Automatically manages standby files when primary changes.	❌ None	Set to AUTO