Create a trigger: In this example, "Field value changed" is used to monitor the "Labels" field for "All issue operations", but other triggers can be used depending on your needs: 

Create an Issue fields condition: In order to trigger the automation, create an "Issue Fields Condition". For example, execute the automation for all Jira issues with the "assets_create_object" added:

Create a Send web request action: To create an object in Assets, we'll use the "Send Web Request" action to perform a POST in the create object REST API:

1. Webhook URL: 

   <JIRA_BASEURL>/rest/assets/1.0/object/create

2. Headers: For creating the <TOKEN> use: Using Personal Access Tokens

   Headers
   Content-Type	application/json
   Authorization	Bearer <TOKEN>

3. HTTP method: POST
4. Webhook body: Custom data
5. Wait for response:  Delay execution of subsequent rule actions until we've received a response for this webhook

6. Custom data: We will use this field as a payload for custom fields that will be used to attribute assets using smart values. For example, two custom text fields are used: "Device Name" and "Vendor Name". The number of custom fields can change, depending on the number of attributes we would like to fill.

   {
       "objectTypeId": 24,
       "attributes": [
           {
               "objectTypeAttributeId": 154,
               "objectAttributeValues": [
                   {
                       "value": "{{Device Name}}"
                   }
               ]
           },
                 {
               "objectTypeAttributeId": 217,
               "objectAttributeValues": [
                   {
                       "value": "{{Vendor Name}}"
                   }
               ]
           }
       ]
   }

     To match your configuration, you'll have to replace the values for objectTypeId and objectTypeAttributeId. - Assets (formerly Insight): How to get the IDs of object schema, object type and object from the Jira User Interface

Create an Edit issue action: Select the Assets custom field which will return the object created

Additional fields: Add the JSON (webhook response smart value will be used to get the object key created) 

{
    "update" : {
        "Host" : [{"add": [{"key" : "{{webhookResponse.body.objectKey}}"}]}]
    }
}

Replace the Host custom field with your Assets custom field - Assets with Jira REST API