Why do I get "no pg_hba.conf SSL is off" when deploying Flask app to Heroku?

I'm following a Udemy course and deploying a Flask app to Heroku. The problem is when I type

heroku pg:psql --app *appname* 

I get :

psql: SSL SYSCALL error: Connection reset by peer (0x00002746/10054)
FATAL:  no pg_hba.conf entry for host "37.125.61.91", user "whlcorobevpteq", database "dcmbbmbl1bbrgd", SSL off

Here is my relevant code:

app.config['SQLALCHEMY_DATABASE_URI']='postgres://whlcorobevpteq:a234a0b5f7300d9f6e43d566b5c849c3b1b20fb8d87ad6b994df2c18b686d624@ec2-174-129-240-67.compute-1.amazonaws.com:5432/dcmbbmbl1bbrgd?sslmode=require'

db=SQLAlchemy(app)