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You can set up auto direct message for new followers, unfollowers, people you follow or unfollow, by clicking on autopilot which is located in your dashboard.
To send DM's to specific users, click on the lists, then select the users and then create a new list, add the desired usernames to the list and go to send message click on userlists and select the userlist you created and on the right side click on custom to add your desired message and send the DMS.
Once you send DMS, all the users you sent out the DMS to will appear in direct messenger, you can chat with them in real time.
Navigate to posts, click on new post to upload your desired image and select the image you want to post and type your message.
It means that you are choosing the wrong method to verify your account,please use the method you have added on Instagram for verification.