it seems it jump to account.docusign.com when open the Docusign application and I also not find any option switch to account-d.docusign.com.

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​@neethujkp ​@Hengfeng Ge--I thought you should be able to access demo, but asked one of the IOS team for confirmation and here is the response: 

“Docusign mobile apps can connect to Demo sandbox environment (https://account-d.docusign.com/). Connecting to any other Sandbox environment is prohibited on production versions of apps. To connect to demo (sandbox), here are the steps:

1. Install app (from App Store) on your device
2. Go to phone's settings -> Apps -> Docusign -> Environments -> select `Demo` from list.”

I hope that works for you, but if not, let us know, please.

Regards,
Jerry