Adding timestamp column

Hi admins, greetings.

I'm trying to add a timestamp column in an existent table.

This query works fine:

select timecreated, timezone('America/Santiago'::text,
to_timestamp(timecreated::double precision)) datecreated
from MDL_LOGSTORE_STANDARD_LOG;

But, when I want to alter the table I get a syntax error

alter table MDL_LOGSTORE_STANDARD_LOG
add column datecreated timestamp
generated always as ( timezone ('America/Santiago'::text,
to_timestamp(timecreated::double precision)));

SQL Error [42601]: ERROR: syntax error at end of input
Position: 185

I would appreciate some tips

Thanks in advanced

kind regards

Mauricio Fernández