This is my StoreLayout (which is not the root layout, and there is another layout function over this one that's exporting a metadata object).

export async function generateMetadata(): Promise<Metadata> {
    const requestHeaders = headers();
    const subdomain = (requestHeaders.get('host') || 'localhost:3000').split('.').slice(0, isProduction ? -2 : -1).join('.');
  
    const result = await getSchoolByStoreURL(subdomain);
   
    return {
      title: (result ? result?.name + ' - ' : '') + 'Nineteen Production',
      description: '',
    }
}

export default function StoreLayout ({ children }: RootLayoutProps) {
    return (
        <div className="pt-[105px]">
            {children}
        </div>
    )
}

This works in Dev, but in production... it creates this error:

.next/types/app/page.ts:32:15
Type error: Type 'OmitWithTag<ResolvingMetadata, keyof PageProps, "generateMetadata">' does not satisfy the constraint '{ [x: string]: never; }'.
  Property 'then' is incompatible with index signature.
    Type '<TResult1 = ResolvedMetadata, TResult2 = never>(onfulfilled?: ((value: ResolvedMetadata) => TResult1 | PromiseLike<TResult1>) | null | undefined, onrejected?: ((reason: any) => TResult2 | PromiseLike<...>) | ... 1 more ... | undefined) => Promise<...>' is not assignable to type 'never'.

  30 | // Check the arguments and return type of the generateMetadata function
  31 | if ('generateMetadata' in entry) {
> 32 |   checkFields<Diff<PageProps, FirstArg<MaybeField<TEntry, 'generateMetadata'>>, 'generateMetadata'>>()
     |               ^
  33 |   checkFields<Diff<ResolvingMetadata, SecondArg<MaybeField<TEntry, 'generateMetadata'>>, 'generateMetadata'>>()
  34 | }
  35 |