Evaluate flags for an end user

{  "flags": [    {      "featureFlagId": "ff_v8b3n5q0w2e7h7d2k9m4x1c6",      "key": "new-checkout",      "isEnabled": true,      "variantKey": null,      "value": null,      "reason": "default",      "ruleId": null    }  ]}

{  "error": {    "type": "invalid_request",    "code": "identity_required",    "message": "Name the end user by personId, distinctId, email or externalIds."  }}

{  "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": "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."  }}