validation

https://docs.getenvie.com/errors/validation · 400 — the request was understood but its values are invalid.

The problem document carries an errors array with one entry per failing field:

{
	"type": "https://docs.getenvie.com/errors/validation",
	"title": "Validation failed",
	"status": 400,
	"errors": [{ "path": "handle", "message": "String must contain at least 1 character(s)" }]
}

Frequent causes

• Missing handle on a save. POST /v1/storefront/wishlist/toggle requires productId and handle — Envie stores identity, and the handle is how storefronts fetch product data later.
• Numeric ids sent as numbers. Shopify's 64-bit ids overflow JavaScript numbers, so the API takes them as strings: "productId": "8123456789012".
• Wrong id prefix. Internal ids are typed: lists are lst_…, items itm_…. Passing one where the other belongs is a 400, deliberately — not a confusing 404.
• No owner on a storefront call. Anonymous requests need an anonymousId; without one and without a logged-in customer there is no wishlist to act on.

Fix

Read errors[].path, correct those fields, resend. Nothing was persisted.