ALLOW-FROMbeing deprecated in the major browsers this is no longer a viable solution for preventing clickjacking in flipbooks. To solve that issue you will have to refer to Content-Security-Policy.
frame-ancestors viewer.ipaper.ioand in the case of you using a branded domain then you should of course use your branded domain instead.
<iframe>and viewed on iOS browsers, will appear too large and hence overflow from its original bounds.
<iframe>elements cannot be restricted by size: declaring explicit width and height in CSS does not work. The browser will instead attempt to size the
max-width: 100vwto the body element of the embedded page, which will force the
<iframe>to be aware of the size of its wrapping container. It effectively places a constraint on the maximum permissible width for the page: