DB LInk not connecting

Oracle Enterprise DB 12.1.0.2

--> I am able to log to SQL plus using:

SQLPLUS TEMP_CP_VALIDATION/VALIDATION2019@VL236DB1

--> I created this database link:

create database link

  TRNBLUEORIGINP_DB1

connect to

  TEMP_CP_VALIDATION

identified by

  VALIDATION2019

using

  'VL236DB1';

--> Database link created

SQL> select * from dual@TRNBLUEORIGINP_DB1;

ERROR at line 1:

ORA-12504: TNS:listener was not given the SERVICE_NAME in CONNECT_DATA