An Office 365 workflow becomes suspended and the only error message in the workflow history is 'Forbidden.'
Grant access to write to the Workflow History list for the SharePoint site to the user account running the workflow. This will allow the workflow to display the true error which can then be used to resolve the underlying issue.
When an O365 subscription has less than 30 days to the end of the subscription a message is written to the Workflow History list advising of this.
This message is written using the permissions of the workflow Initiator. If the workflow has an action set as the first action configured to run with elevated permissions the message will still be written with the Initiators account. If the Initiator does not have access to the Workflow History list in this scenario the workflow will suspend with an access error.