I'm using MSAL.js to acquire a silent token and it works ok when i login See my snippet code below
var userid = _spPageContextInfo.userId;
//console.log(email);
var upn = getUserEmailByLoginName(userid);
var config = {
auth: {
clientId: "",
authority: "https://login.microsoftonline.com/techie.onmicrosoft.com"
redirectUri: "someUrl",
},
cache: {
cacheLocation: "localStorage"
}
};
var requestPermissionScope = {
scopes: ["user.read"],
loginHint: upn,--setting the email address here e.g joe@xyz.com (is this the loginHint?
//extraQueryParameters: {domain_hint: 'organizations'}
};
The issue i'm facing though is when another user logs in the get this error below
ClientAuthError: User login is required. For silent calls, request must contain either sid or login_hint

In regards to the loginHint. What value do we need? Is it an email address?
In this article
it says prefered_username. But what is it?
Thanks in Advance