Set who gets a flag in an environment

{  "id": "ff_v8b3n5q0w2e7h7d2k9m4x1c6",  "projectId": "proj_tz4a98xxat96iws9zmbrgj3a",  "key": "new-checkout",  "description": "The redesigned checkout screen.",  "type": "boolean",  "environments": {    "production": {      "isEnabled": true,      "overrides": [        {          "identityType": "email",          "identityValue": "ada@example.com",          "isEnabled": true,          "variantKey": null,          "note": "QA device for the new checkout"        }      ],      "rules": [        {          "id": "beta-testers",          "name": "Beta testers",          "identities": [            {              "identityType": "distinct_id",              "identityValue": "user_8231"            }          ],          "serve": {            "rolloutPercentage": 100,            "variantKey": null          }        }      ],      "fallthrough": {        "rolloutPercentage": 50,        "variantKey": null      }    },    "test": {      "isEnabled": true,      "overrides": [],      "rules": [],      "fallthrough": {        "rolloutPercentage": 100,        "variantKey": null      }    }  },  "isArchived": false,  "experimentId": null,  "createdAt": "2026-02-24T10:12:45.000Z",  "updatedAt": "2026-03-14T09:00:00.000Z"}

{  "error": {    "type": "invalid_request",    "code": "invalid_environment",    "message": "The flag has no variant annual-first."  }}

{  "error": {    "type": "unauthenticated",    "code": "invalid_api_key",    "message": "This secret key is not valid."  }}

{  "error": {    "type": "permission_denied",    "code": "permission_denied",    "message": "Insufficient permissions."  }}

{  "error": {    "type": "not_found",    "code": "project_not_found",    "message": "There is no project proj_tz4a98xxat96iws9zmbrgj3a, or this credential cannot use it.",    "param": "projectId"  }}

{  "error": {    "type": "conflict",    "code": "feature_flag_managed_by_experiment",    "message": "Feature flag ff_k9m4x1c6v8b3n5q0w2e7h7d2 assigns the arms of experiment exp_c6v8b3n5q0w2e7h7d2k9m4x1; change it through the experiment."  }}

{  "error": {    "type": "internal",    "code": "internal_error",    "message": "Something went wrong on our side. Try again, and contact support with the Request-Id header if it keeps failing."  }}