Extending/External custom fields not showing selections

I have followed the instructions and even used the sample from Extending/External custom fields - RT 5.0.3 Documentation - Best Practical
the problem is I can see the new entry but selection box stays empty with no selection or box.

Can you show what the external source looks like?

Hello and thanks for replying, below is what I used.

actual values provider method

sub ExternalValues {
# return reference to array ([])
return [
# each element of the array is a reference to hash that describe a value
# possible keys are name, description, sortorder, and category
{ name => ‘value1’, description => ‘external value’, sortorder => 1, category => ‘Other CF’ },
{ name => ‘value2’, description => ‘another external value’, sortorder => 2, category => ‘Other CF’ },
# values without description are also valid, the default description is empty string
{ name => ‘value3’, sortorder => 3 },
# you can skip sortorder too, but note that the default sortorder is 0 (zero)
{ name => ‘value3’ },