pg_dump mismatch

As I described my confusion in an earlier post, I installed a Phoenix app with fly launch, and it asked if I wanted a Postgres Db and addded it for me; hence I have my-app and my-app-db (with internal address only).

I want to pg_dump from my_app_db, and I finally figured out that – as a last resort, not a production solution – I could simply do this in my-app:

flyctl ssh console

apt-get update
apt-get install postgresql-client

pg_dump --username=postgres --dbname=my-app --port=5432 --host=my-app-db.internal 

Only to discover:

pg_dump: error: server version: 14.1 (Debian 14.1-1.pgdg110+1); pg_dump version: 13.5 (Debian 13.5-0+deb11u1)
pg_dump: error: aborting because of server version mismatch

Then I went down a rabbit hole of
apt-get install postgresql-client-14 …and endless missing libs, to try to solve this, but it seems futile.

Is there a reason why my-app-db is on v. 14 whereas my-app repositories have only v. 13?

Or is there a simple way to accomplish my goal of getting the dump file?