Which version of ElastiFlow are you running? They typically come with an ILM policy. Are you using ECS? If not, this policy won’t work.
Here’s the JSON for the ‘elastiflow’ ILM that comes with ElastiFlow 7.2.2. Since I am using CODEX this ILM policy will be applied to all indices that match the ‘elastiflow-*-codex-*’ name pattern.