elastic beanstalk Configuration validation exception: Invalid DBEngineVersion - how to resolve?

Hello all! I am trying to add a database to an elastic beanstalk environment using the eb console (as directed by the docs). However, when I load the configuration page, or go into the Database | Edit tab, the page shows the error below and doesn't show the database creation form.

Configuration Validation Configuration validation exception: Invalid option value: '5.6' (Namespace: 'aws:rds:dbinstance', OptionName: 'DBEngineVersion'): Engine Version 5.6 not supported for mysql db

This error only started appearing yesterday. I have tried a few times, including deleting the environment completely and restarting from scratch. Same error. Has something changed on the AWS side? Is there something I can do to resolve this?

As far as I can tell I have no RDS configs in my local set up (I'm using the eb cli). FWIW I was intending to add a postgresql db.

I was using eb as a way of bootstrapping my way into AWS, and then moving on to a straign CloudFormation setup. Is there a way of setting up an RDS instance independently and then connecting it to an eb environment?

Many thanks!