So it looks like iOS Safari is not liking the code that seems to work everywhere else. The best way to find out what it doesn't like then would be to use whatever version of "developer tools" the browser has to see if a script is not being loaded or a component of the iFrame, or something completely different like a problem with cross-domain cookie access.
If it is a cross-domain issue, then it is not unique to you, as S/O has a few questions on this topic also.... I would suggest you read through these and their linked resources to see if one of the presented solutions will work for you.
1:
p3p - safari does not allowed cross-domain cookies in iframe - Stack Overflow[
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2:
javascript - Setting cross-domain cookies in Safari - Stack Overflow[
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