Specify criteria for DM approval
The terms of Twitter says that when sending a DM to a user via the Twitter API, you must obtain the user's permission.
I agree with this rule, but the criteria are not specified.
The rules say that the followings are not the permission.
1. Mutual follow
2. DM can be sent
Now, specify which other method to use for authorization.
Thanks for your feedback!
We are intentionally open-ended in our documentation about this, because opt in can take any of a number of different forms. For example, a user could DM you first, or opt in using a public Tweet. We don’t narrowly define it because auto-response campaigns can take a lot of different forms.
If you have any Policy-related questions, this form is available for you to reach out to our Policy team: https://help.twitter.com/forms/platform (select "I have an API policy question not covered by these points").