Update Customer language (locale) with Shopify Flow & Send HTTP Request

I tested in postman…this is a working example. You are missing at least one bracket (after customerUpdate).

{"query":"mutation updateLocale($input: CustomerInput!) {\n    customerUpdate(input: $input) {\n        userErrors {\n            field\n            message\n        }\n        customer {\n            id\n            locale\n        }\n    }\n}","variables":{"input":{"id":"gid://shopify/Customer/20952568692758","locale":"en"}}}