I followed this guide in order to upgrade the plan for postgres:
I want to upgrade using heroku addons:upgrade.
this is the output:
Changing postgresql-rernd-166744 on myapp-api from heroku-postgresql:hobby-dev to heroku-postgresql:standard-0... !
! An error was encountered when contacting the add-on partner to change to heroku-postgresql:standard-0:
! heroku-postgresql does not currently support changing plans.
I have added a bank card and already using another heroku plan in another app so I doubt that's the reason.