I also get this error when I run your code, which is a copy of the code in GD::SVG for which the module author states:

Finally, here is a fully worked example of using the GD::Simple module to make the syntax cleaner:

This should be reported as an issue.

I was able to run this code example from the POD without error:

use GD::SVG;
my $img   = GD::SVG::Image->new(500,500);
my $white = $img->colorAllocate(255,255,255);
my $black = $img->colorAllocate(0,0,0);
my $blue  = $img->colorAllocate(0,0,255);
my $red   = $img->colorAllocate(255,0,0);
 
$img->startGroup('circle in square');
$img->rectangle(100,100,400,400,$blue);
 
$img->startGroup('circle and boundary');
$img->filledEllipse(250,250,200,200,$red);
$img->ellipse(250,250,200,200,$black);
 
$img->endGroup;
$img->endGroup;
 
print $img->svg;
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