How do I restore my Heroku pg_dump on DigitalOcean?
It looks like you have already restored this data once before, so the objects already exist.  And trying to load it into the database named 'postgres' is a dubious practice anyway.

You should create a new database with a different name and load the data into that new database instead of into 'postgres'.  Or maybe you meant to use the -C option, in which case it will create and use the database which is named inside the dump file as the database to load the data into (in which case the database named in -d is only used to connect to in order to issue the CREATE DATABASE command).

If you really want to load this data to the database named 'postgres', you could use the -c option (without -C), which will drop the existing objects before recreating them.