Embedding MSign portal within an iframe

Hi all,

I'm trying to embed the mSign portal (https://unitfly.msign.si/) within an iframe in a dashboard. The form renders correctly, but when I enter my login details and submit the form, it reloads the empty login form instead of following the redirect to the portal.

Has anyone experienced similar issues with iframe not handling redirects properly, or are there any known workarounds for this kind of issue?

Thanks in advance!