When your template variable is inside a <TMPL_LOOP> you have to qualify it with the loop name:

$template->param(
        chassis_type => [{
                chassis_id => [{
                        SLOTNAME => 'test-slot-name'
                }]
        }]
);

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The template doesn't demand a global SLOTNAME value, it requires a value for every iteration of the loop.

In reply to Re: HTML::Template not finding parameter in template by Loops
in thread HTML::Template not finding parameter in template by bowei_99

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