I am trying to use the SP-API Event Bus notifications.
During configuration I am getting an error.
From the Notifications Use Case Guide here:
https://developer-docs.amazon.com/sp-api/docs/notifications-api-v1-use-case-guide#tutorial-set-up-notifications-amazon-eventbridge-workflow
Step 2, part 5, when I click “Associate with event bus”, I get the error

Could not associate the event source to the event bus

I am having trouble figuring out why.
Anyone been through this?