Heroku's “pg:psql” command doesn't work. How to pass commands to load schema from structure.sql?

I want to load schema from structure.sql file to Heroku's database. On my localhost machine I do as follows and all works just fine, all tables are created:

C:\> psql -U postgres -a -d MyApp_development -f C:\MyApp\db\structure.sql

But when I want to perform the same task on Heroku, it suddenly says ! App not found, although I provide all correct commands and data.

First of all, I get my credentials:

C:\Heroku\MyApp>heroku pg:credentials DATABASE

Then I do copy/paste credentials and run the command but get App not found: