In order to Tout through Gmail, a draft of the email has to exist in Gmail.
Since the email address is getting auto-populated and you are selecting a campaign or template which just automatically inserts the content, no edit is being made to the email. This means it's not triggering a draft to be created which is why you are unable to Tout.
The way around this, is if you insert a template/campaign and add a word or a space to the body of the email and delete it, it will trigger the draft being created and then you will be able to Tout it.
Alternatively you can use the Email with Tout or Add to Tout Campaign buttons on the contacts/leads and reach out that way.