I have clients from all around the world, but I only use USA proxies to manage all with MassPlanner.
They can be in china, logged into their account, while I am managing it using MassPlanner on a USA proxy.
Here is the steps that I do:
I tell the client, "I will attempt to login now. There is a possibility my login attempt may be flagged as suspicious because I am logging in to your account from a different country/network. If this happens, I will need you (the client) to login to your account, and click "It Was Me". This will tell Instagram that the login attempt was not suspicious, and I can then begin to manage your Instagram account."
"WARNING: If you click "It Was Not Me" I will never be able to manage this Instagram account."
This will make it look like the Instagram account is being shared between 2 friends who live in different areas.
Whatever you do, NEVER phone verify their account when you first login. You need your client to click "It Was Me".
Disclaimer: What works for me, may not work for you. So please proceed with caution.