Update Image of Product Variant

How does one update a variant image?

The documentation shows how to create a new product with images by populating images_attribute (POST).

Following this example, I have tried updating (PUT) images_attribute… (I have tried to both pass a product_id and display_order value as part of the update) but this does not seem to work. For example:

{"product":{"product_variants_attributes":[{"upc_code":"843953346708","id":34077743}],"id":15823855,"images_attributes":[{"src":"https://dev-static.exampleurl.com/media/catalog/product/2/0/20270r_1_1.jpg","product_id":34077743}]}}

I have also tried defining the main_image property inside the associated product variant as part of the update…

{"product":{"product_variants_attributes":[{"upc_code":"843953346708","id":34077743,"main_image":{"src":"https://dev-static.exampleurl.com/media/catalog/product/2/0/20270r_1_1.jpg"}}],"id":15823855}}

At this point, I am not sure what else to try or what I am doing wrong…?