SOLVED I found a typing error in the reference to the hash with the URL.

And the typo was? I bet on

- $snapshot-> url( "IPCamera{$key}");
+ $snapshot-> url( "$IPCamera{$key}");
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BTW there's no need to put that into double quotes, or is there? if you had written

$snapshot-> url( IPCamera{$key});
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the compiler would have catched that error.