Updating Custom Properties for Product Variants

I’m trying to update custom properties for product variants using a PUT request to https://api.veeqo.com/products/product_id.

The product currently has the property “Colour” with the value “Pink”; I’d like to be able to update existing or create new properties.

If I make a simple call to update a variant title, that works, e.g.:

{
   "product":{
	  "product_variants_attributes":[
		 {
			"id":35308545,
			"title":"LARGE - Variant Updatedc"
		 }
	  ]
   }
}

However, if I make a call like this (variant_property_specifics properties copied from the response to a GET https://api.veeqo.com/products/product_id request, value changed from “Pink” to “Blue”) I get a 500 / Internal Server Error response:

{
   "product":{
	  "product_variants_attributes":[
		 {
			"id":35308545,
			"title":"LARGE - Variant Updateda",
			"variant_property_specifics":[
			   {
				  "id":12845834,
				  "product_specific_id":12545926,
				  "product_property_id":80471,
				  "product_property_name":"Colour",
				  "value":"Blue"
			   }
			]
		 }
	  ]
   }
}

Is updating properties unsupported, or do I have an error in my update JSON?