Currently I have a feature flag with a rollout strategy that uses a specific stickness parameter (accountId)
I set it to 25% rollout and I'm wondering if there's a way to fetch all the accountIds that are included in the rollout.
I'm expecting to have an API exposed where we can provide the feature-flag and it would return the results or something
This is not possible due to the way Unleash evaluates feature flags. This data is not stored in Unleash, and instead only used for feature flag evaluation.
This is one of Unleash's 11 principles for building and scaling feature flag systems. See: 2. Never expose PII. Follow the principle of least privilege.
You can also learn more about how stickiness is deterministically calculated here: https://docs.getunleash.io/reference/stickiness#calculation
Depending on your exact needs you could potentially collect this data by using Impression data in your application.