Problem with creating metafield of type weight

Retired Boards Appdev Metafields
1

I have been using the Shopify REST API 2024-01 to create/update/delete Product Meta Fields no problem.

These have all been multi-line-text type.

When my same code tries to create a Variant Meta Field of type “weight” then I get an error 422 with no error message.

URL is:

/admin/api/2024-01/variants/9999/metafields.json

My submitted data is:

{"metafield":{"namespace":"custom","key":"weight","value":{"value":"360.0","unit":"g"},"type":"weight"}} 

I have read that 422 implies poorly formatted request, but it is the same request format that is working for Product Meta Fields and Multi Line Types.

Can you see what is wrong? Could ‘weight’ be a reserved word? Is there a way of ‘seeing’ what the server is receiving to give a clue to the problem?