Issue
In Heroku Connect, I would like to enable writes for a Salesforce Object object but I get the message "This object is read-only and does not support writing to Salesforce."
Resolution
Heroku Connect "read-only" errors are most commonly a symptom of missing permissions on a Salesforce user or organization.
You can find a list of Supported Objects for your instance of Heroku Connect at: https://connect.heroku.com/supported-objects. Please note that the list of supported objects differs from instance to instance based on what kind of Salesforce configuration you have.
Once you've confirmed that the object is listed on the Supported Objects page, look it up the in the Salesforce Object API Reference to see what conditions apply for the object to be writable on the Salesforce API.
If you've confirmed that your Salesforce instance is up to spec to allow writing from Heroku Connect to Salesforce, reach out to Support. We'd be glad to assist you in debugging the issue.