Update your env.ts in the sanity file like this first

export const apiVersion = process.env.NEXT_PUBLIC_SANITY_API_VERSION || '2024-09-30'

export const dataset = assertValue( process.env.SANITY_STUDIO_DATASET || process.env.NEXT_PUBLIC_SANITY_STUDIO_DATASET, 'Missing environment variable: SANITY_STUDIO_DATASET or NEXT_PUBLIC_SANITY_STUDIO_DATASET' )

export const projectId = assertValue( process.env.SANITY_STUDIO_PROJECT_ID || process.env.NEXT_PUBLIC_SANITY_PROJECT_ID, 'Missing environment variable: SANITY_STUDIO_PROJECT_ID or NEXT_PUBLIC_SANITY_PROJECT_ID' )

function assertValue(v: T | undefined, errorMessage: string): T { if (v === undefined) { throw new Error(errorMessage)

}

return v }

And in your env.local and the .env file write :

SANITY_STUDIO_DATASET=production

SANITY_STUDIO_PROJECT_ID=*********

NEXT_PUBLIC_SANITY_STUDIO_DATASET=production

NEXT_PUBLIC_SANITY_PROJECT_ID=**********

After thoses changes you will not get that error again