type "xxxxxxx" does not exist

Hello,

I hope this is the right list for me to ask questions about psql.
Please let me know if I am in the wrong place. :)

I am far from an advanced user of PostgreSQL, so please bear with me ...

I am working with an inherited database/codebase. I am trying to call
this function via psql:

# SELECT * FROM functionName('xxxxxxx', 'xxxxxxx', 'xxxxxxx');

What I get back is this:

ERROR: type "xxx_xxx_xxxxx" does not exist
LINE 1: DECLARE results xxx_xxx_xxxxx;
^
QUERY: DECLARE results xxx_xxx_xxxxx;
.....
.....

When listing the functions, I see that functionName() does exist in
the database.

The type also exists (I think):

# select exists (select 1 from pg_type where typname = 'xxx_xxx_xxxxx');
exists
--------
t
(1 row)

Note that the role that owns the 'type' is not the same user that is
calling the "functionName()" from the psql prompt. When I try to
switch roles, using:

sudo -i -u username
psql -U otherusername -d database

… I get:

psql: FATAL: Peer authentication failed for user "otherusername"

Do I need to create a Linux user to login as "otherusername" so I can
test calling the functionName() with xxx_xxx_xxxxx type?

Lastly, the type was declared in the SQL dump like this:

CREATE TYPE xxx_xxx_xxxxx AS (
....

);
ALTER TYPE xxx_xxx_xxxxx OWNER TO otherusername;

I know that's a lot of info ... More than anything, I'm just wondering
if someone can give me tips on where to focus my attention in terms of
trouble shooting?

Thanks so much!