vRA 7.6 - changing the value of a custom property on a Cafe Deployment

During initial provisioning, I add a custom property with a value to the deployment. The property is defined in the Property Dictionary and assigned to a machine blueprint.

When the deplyoemnt is progressing, I need to change the value of this property. I have tried 2 approaches:

1. Using REST:

          PUT query: /catalog-service/api/consumer/deployments/{deployment_id}, with body {"customProp":"value"}

2. Using the Orchestrator REST client:

          restClient = vraHost.createRestClient("com.vmware.csp.core.cafe.catalog.api");

          var props = new Properties();

          props.put("customProp","value");

          var response = restClient.put("/consumer/deployments/{deployment_id}", props);

I get a success response using both methods, but the change is not made in vRA, there is stil lthe old value of the property.

Also, what I have discovered afterwards is, that even when I dump the whole Deployment configuration using the API, the custom  property is nowhere to be found.

Can someone please give me any tips on this?