The app has been hosted on the webdl.onfirstup.com domain, specifically so that it can be accessible in Mainland China. If installing an APK downloaded from https://webdl.onfirstup.com/chinese_privacy_policy.html (direct link to download: https://webdl.onfirstup.com/app-flavor_firstup-cn-debug-signed.apk) is resulting in an error, then this is likely to be a restriction specifically on corporate devices or your organization's VPN. 

Solution

To solve this, it is recommended that a member of your organization's IT team downloads the APK app file and instead hosts this on your intranet for Mainland China so that it can be ensured that app downloads from this site are allowed. This solution has been confirmed to work for customers encountering similar errors when members attempted to download the app directly from Firstup on personal devices. A QR code can then be generated which links to your own site to make it easier for deskless workers to download the app.

It would be your organization's responsibility to ensure that the app is kept up to date by downloading the latest version and rehosting this on your intranet. To be notified when a new mobile version is released, sign into the Firstup Help Center and click Follow on the Release Notes page.