how to write lpad function in PostgreSQL

I’m converting oracle to PostgreSQL. While converting for this below line

P_OTP := LPAD(W_OTPNUM, 6, '0');

I’m getting error like function lpad(integer, integer, unknown) does not exist.
Please help me to solve this error

>Solution :

W_OTPNUM seems to be a number. You cannot pad a number, only a string.

LPAD(W_OTPNUM::TEXT, 6, '0')