A few of our users have been experiencing issues adding Instagram services.
This is due to a general issue on Instagram's end which is affecting a number of third party sites like Sendible.
Instagram are aware of the error and are currently looking to resolve the issue but it may still take some time.
We are in contact with them and will update this article once we hear more from them.
Update - 12/29/2016
Instagram appears to have resolved the issue on their end meaning users should now be able to set up Instagram services again without issue. Please submit a ticket if you encounter any further issues with this.