Authorization failed when running purgeSolrSynoymns for an Acquia Search environment

Problem/Motivation

When exporting new synonyms to Acquia Cloud Search, the following error occurs:
Client error: `DELETE https://[domain]/solr/[env-id]/schema/analysis/synonyms/english/[synonym]` resulted in a `403 Forbidden`
response:
Authorization Failed

However, adding terms works fine if I comment out the line of code: $this->purgeSolrSynoymns($solr_connector);

Steps to reproduce

1. Create new synonyms
2. Click the "Import to Solr" button OR run the following drush command: drush ssolr-syn-ex --plugin=solr_uploader --langcode=en

Proposed resolution

Maybe there would be a way to use the Solr connector rather than a POST request so that the connection is made before sending the query, but I can't figure out how to do it.