Instagram app review rejection help

We have attempted the Instagram app review process 4 times and been rejected each time but the reasons for this are opaque. We do not believe there is a problem with the app (it's approved for use with messenger already), but rather some issues around the app review process and access/test mode.

We are looking for someone with experience in getting successful Instagram app reviews done in order to help us get the app approved.

Thank you for your assistance and time - I appreciate it and cannot wait to hear your feedback!