Add people to a cohort

{  "cohort": {    "id": "an_cohort_m2x7c1q8w4e6r0t5y2u8k3v9",    "projectId": "proj_tz4a98xxat96iws9zmbrgj3a",    "name": "Beta testers",    "description": null,    "kind": "static",    "definition": null,    "memberCount": 1,    "createdAt": "2026-03-05T12:00:00.000Z",    "updatedAt": "2026-03-14T09:26:53.000Z"  },  "added": 1,  "unresolved": [    "grace@example.com"  ]}

{  "error": {    "type": "invalid_request",    "code": "invalid_analytics_cohort",    "message": "Cohorts name each other in a circle: Power users names Lapsed, which names Power users."  }}

{  "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."  }}

{  "error": {    "type": "unavailable",    "code": "string",    "message": "string",    "param": "string"  }}