Hey there!
I am having the exact same issue. Nothing I do is helping.
Here is the code I am using.
<iframe src="https://matrix.crmls.org/Matrix/public/IDX.aspx?idx=8ee92f4d" width="100%" height="100%" frameborder="0" marginwidth="0" marginheight="0"></iframe>
I am trying to add ppadding but nothing works.
Help!