Idea validation - Email forwarding

The problem being solved:
Forwarding customer purchase notification from various ecommerce platform (wordpress, shopify, squarespace, etc...) to a device via email, text messaging and others (if necessary).

Context:
This is a problem I ran into while building a ecommerce project for a client using wordpress and woocommerce.

Question:
How do I go about answering the following questions below, do I email a set of people that I think will benefit from this solution or do I create a landing page for this solution?

Questions that I'm seeking answer for:

1. How do I validate this idea? I can ask the client if this a something that they are willing to pay for? Ask other similar clients if they are having the same problem?

2. How do I determine if other people are facing the same problem?