AVD Webclient using wrong identity

I am building a solution to provide a published app to external users (mind you, external to my company, not external to my AAD). Since these are external users, most of them are already using some form of M365 services in their browser and are signed in to those when connecting to the AVD web client. We are able to send them to the proper sign in page for the identity (let's say contoso.com) they are provided with for this remote-app, however after signing in they are prompted with the following error:

"It looks like your system administrator hasn’t set up any resources for user1@adatum.com yet. Please choose a different account or try again. If you believe you have received this message in error, please contact your system administrator."

There subsequently is no way to switch to the contoso.com identity they literally just signed into, at least from the GUI. 

When using an incognito browser everything works fine, however, since this remote-app solution is presented to the userbase from the environment of the customer (adatum.com) with the hyperlink presented to them in an environment where they need to be signed in to adatum, it is very undesirable to ask them to switch to incognito every time they want to open the app.

So what I want to know if there's any way to force the AVD webclient to use a certain identity for the session. Maybe a hidden url parameter we can add to the hyperlink similar to the domain hint for the oauth-process?