env variable fails for enum type

/**
 * Specify your client-side environment variables schema here.
 * This way you can ensure the app isn't built with invalid env vars.
 * To expose them to the client, prefix them with `NEXT_PUBLIC_`.
 */
export const clientSchema = z.object({
  NEXT_PUBLIC_APP_URL: z.string(),
  NEXT_PUBLIC_AWS_S3_BUCKET_NAME: z.string(),
  NEXT_PUBLIC_EMAIL_VERIFICATION: z
    .enum(["OPTIONAL", "REQUIRED"])
    .default("OPTIONAL"),
});

/**
 * You can't destruct `process.env` as a regular object, so you have to do
 * it manually here. This is because Next.js evaluates this at build time,
 * and only used environment variables are included in the build.
 * @type {{ [k in keyof z.infer<typeof clientSchema>]: z.infer<typeof clientSchema>[k] | undefined }}
 */
export const clientEnv = {
  NEXT_PUBLIC_APP_URL: process.env.NEXT_PUBLIC_APP_URL,
  NEXT_PUBLIC_AWS_S3_BUCKET_NAME: process.env.NEXT_PUBLIC_AWS_S3_BUCKET_NAME,
  NEXT_PUBLIC_EMAIL_VERIFICATION: process.env.NEXT_PUBLIC_EMAIL_VERIFICATION,
};

/**
 * Specify your client-side environment variables schema here.
 * This way you can ensure the app isn't built with invalid env vars.
 * To expose them to the client, prefix them with `NEXT_PUBLIC_`.
 */
export const clientSchema = z.object({
  NEXT_PUBLIC_APP_URL: z.string(),
  NEXT_PUBLIC_AWS_S3_BUCKET_NAME: z.string(),
  NEXT_PUBLIC_EMAIL_VERIFICATION: z
    .enum(["OPTIONAL", "REQUIRED"])
    .default("OPTIONAL"),
});

/**
 * You can't destruct `process.env` as a regular object, so you have to do
 * it manually here. This is because Next.js evaluates this at build time,
 * and only used environment variables are included in the build.
 * @type {{ [k in keyof z.infer<typeof clientSchema>]: z.infer<typeof clientSchema>[k] | undefined }}
 */
export const clientEnv = {
  NEXT_PUBLIC_APP_URL: process.env.NEXT_PUBLIC_APP_URL,
  NEXT_PUBLIC_AWS_S3_BUCKET_NAME: process.env.NEXT_PUBLIC_AWS_S3_BUCKET_NAME,
  NEXT_PUBLIC_EMAIL_VERIFICATION: process.env.NEXT_PUBLIC_EMAIL_VERIFICATION,
};