Using metadata fields in email

[Messmeriza]

I have created a custom data field at the variant level with namespace & key called 'custom.pkglength'.

I am editing the HTML body of an automated email being sent for fulfilment and having trouble figuring out how to reference this field in the email, can anyone assist in how to correctly reference metadata fields at the variant level?

I have tried

{{ line.variant.metafields.custom.pkglength }}

{{ line.line_item.metafields.custom.pkglength }}

but these don't work