The product message isn't showing up.

1. The product message for the specific rule is blank.

The initial product message input form only shows a placeholder, but nothing is actually entered. Please keep this in mind. 

If this is the cause, try entering the product message and check again.

2.The embedded app isn't activated.

If this is the cause, activate the embedded app and check again.

3. The collection set for the targeted product is not public.

In our app, if the collection is not public, the product message doesn't show up because the frontend process can't access the collection information. However, the purchase restriction check works properly since it's a server-side process, which can access collection information even if it's not public. 

If this is the cause, please consider one of the following actions:

• Set the relevant collection to public status.

• Remove the collection from the quantity rule and specify the product in question (or specify a collection that is public).