See this page for more details about the Configsets API:
https://solr.apache.org/guide/solr/latest/configuration-guide/configsets-api.html

• HTTP Request (URL):
  ► V1 API:
  http://localhost:8983/solr/admin/configs?action=List&omitHeader=true&wt=xml&indent=true
  
  ► V2 API:
  http://localhost:8983/api/cluster/configs?omitHeader=true&wt=xml&indent=true
  
  These parameters can be added to the request:
  
  • omitHeader=true
    
    
  • wt=json
    
    
  • indent=true
    
  
  
• Java sample:
  private void listConfigSets(final int jettyPort) throws IOException { final String url = "http://localhost:" + jettyPort + "/solr/admin/configs?action=LIST"; final HttpGet request = new HttpGet(url); try (final CloseableHttpClient client = HttpClientBuilder.create().build(); final CloseableHttpResponse response = client.execute(request)) { final HttpEntity entity = response.getEntity(); System.out.println(IOUtils.toString(entity.getContent(), "UTF-8")); // close the content stream. EntityUtils.consumeQuietly(entity); } }

To upload a Configset, you need to prepare the zip file that has to be created from within a directory where the solr configuration files ("solrconfig.xml", ...) are directly located. Solr configuration files must be the top level entry in the zip file.

Create the zip file:
$ (cd /opt/solr/server/solr/configsets/_default/conf && zip -r - *) > /opt/solr/_defaultUploadedConfigSet.zip
Upload the zip file and create a Configset:
$ curl -X POST \ --header "Content-Type:application/octet-stream" \ --data-binary @/opt/solr/_defaultUploadedConfigSet.zip \ "http://localhost:8983/solr/admin/configs?action=UPLOAD&name=_defaultUploadedConfigSet"
You can use this command if you want to create and upload the zip file and create the Configset at the same time:
$ (cd /opt/solr/server/solr/configsets/_default/conf && zip -r - *) | curl -X POST \ --header "Content-Type:application/octet-stream" \ --data-binary @- \ "http://localhost:8983/solr/admin/configs?action=UPLOAD&name=_defaultUploadedConfigSet1"

Create a new Configset ("configSetName") based on an existing Configset ("baseConfigSetName").

The Configset can be created as immutable ("configSetProp.immutable=true"), which means it cannot be edited or deleted and its Schema cannot be updated by the Schema API.

• HTTP Request (URL):
  ► V1 API:
  http://localhost:8983/solr/admin/configs?action=CREATE&name=_default1&baseConfigSet=_default&configSetProp.immutable=false
  
  ► V2 API:
  $ curl -X POST -H 'Content-type: application/json' \ -d '{ "create":{ "name": "_default2", "baseConfigSet": "_default" } }' \ http://localhost:8983/api/cluster/configs?configSetProp.immutable=false
  
• Java sample:
  private void createConfigSet(final int jettyPort, final String configSetName, final String baseConfigSetName) throws IOException { final String url = "http://localhost:" + jettyPort + "/solr/admin/configs?action=CREATE" + "&name=" + configSetName + "&baseConfigSet=" + baseConfigSetName + "&configSetProp.immutable=false"; final HttpGet request = new HttpGet(url); try (final CloseableHttpClient client = HttpClientBuilder.create().build(); final CloseableHttpResponse response = client.execute(request)) { final HttpEntity entity = response.getEntity(); System.out.println(IOUtils.toString(entity.getContent(), "UTF-8")); // close the content stream. EntityUtils.consumeQuietly(entity); } }

You will get an error if you try to delete a Configset that is used by collections.
You have to delete those collections to be able to delete the Configset.

• HTTP Request (URL):
  ► V1 API:
  http://localhost:8983/solr/admin/configs?action=DELETE&name=_default1
  
  ► V2 API:
  $ curl -X DELETE http://localhost:8983/api/cluster/configs/_default2
  
• Java sample:
  private void deleteConfigSet(final int jettyPort, final String configSetName) throws IOException { final String url = "http://localhost:" + jettyPort + "/solr/admin/configs?action=DELETE" + "&name=" + configSetName; final HttpGet request = new HttpGet(url); try (final CloseableHttpClient client = HttpClientBuilder.create().build(); final CloseableHttpResponse response = client.execute(request)) { final HttpEntity entity = response.getEntity(); System.out.println(IOUtils.toString(entity.getContent(), "UTF-8")); // close the content stream. EntityUtils.consumeQuietly(entity); } }