Intuit Link is not device dependent and runs off the same website whether it's accessed via a computer or mobile phone.  That's why Intuit retired the old Apps for Link some years back.

The most important thing is to make sure your client do the following:

• Use only an Intuit Link supported browser (https://proconnect.intuit.com/community/help-articles/help/system-requirements-for-intuit-link/00/55...);
• Always open Intuit Link in iincognito mode only.

Intuit Link is a bit temperamental and users can avoid most common problems by taking these steps.

Before your client tries again, it'd be best to clear the cache and cookies as well as restart the browser/pc/device.

If the problem persists, it probably has to do with some settings, security or otherwise, on that pc/device.