Only changing the settings with the following command did not work in my environment:
curl -XPUT -H "Content-Type: application/json" http://localhost:9200/_all/_settings -d '{"index.blocks.read_only_allow_delete": null}'
I had to also ran the Force Merge API command:
curl -X POST "localhost:9200/my-index-000001/_forcemerge?pretty"
ref: Force Merge API