Posting to Instagram on the the platform works a bit differently than the rest of the social media platforms. Instagram does not allow 3rd party API connections like all of the social media platforms do, so posting to the popular social media account take an extra step.
Follow these instructions, and you'll be posting to Instagram like a champ.
First, connect your Instagram account through the "Add Services" section. In the dialog, you’ll see the Instagram Post option. Click Setup.
You’ll be prompted to connect to your Instagram account. Follow the steps.
After connecting, you’ll be able to specify one or more email recipients that will receive email notifications when your Instagram picture needs to be uploaded.
Click Save Settings and the service will now appear within your account.
To post to Instagram, click Compose and select your Instagram Post service from the list. Choose a date and time to have this post go out.
At the scheduled the time, an email will be sent to the recipient(s) you specified during setup, notifying them that the attached image needs to be uploaded to Instagram.
It's a little different than the ease of the other social media profiles available, but it's still a good way to manage, and engage with your Instagram followers.