Postgres 11 Insufficient columns in PRIMARY KEY constraint definition

DETAIL: PRIMARY KEY constraint on table lacks column "sdate" which is part
of the partition key. SQL state: 0A000

I have a table which i am trying to create with RANGE partitioning using
the timestamp column. But my primary doesnot need to have this timestamp
column, its another column. Why is postgres 11 asking me to add this
partition key in the primary key ?

The documentation lacks this or am missing something ?