Form: Binding input to sub-schema "Can only bind to an Identifier or MemberExpression"

[Extarys]

I have this simple schema:

export const formSchema = z.object({
  name: z.string().min(2).max(200),
  owner: z.object({
    firstName: z.string(),
    lastName: z.string(),
  }).optional(),

});

When I try to bind a field to firstName I get an error I'm unfamiliar with.

The input:

	<Form.Field {form} name="firstName">
		<Form.Control let:attrs>
			<Form.Label>Prénom</Form.Label>
			<Input {...attrs} bind:value={$formData.owner?.firstName} />
		</Form.Control>
		<Form.FieldErrors />
	</Form.Field>

The error:

Can only bind to an Identifier or MemberExpression

I superficially understand what that means, but no idea how to fix it.

Any thoughts?