How to accept incoming webhooks?
This is nitech from the future. You need to read up a bit. While you built RC Planes from FliteTest with your kids, I went ahead and read up a bit for you: 

Webhooks is a concept, not a technology 

Webhooks are to apps what push notifications are to us. Remember when you had to check your email to know if there was a new mail? Not any more. Technically speaking, webhooks are "user-defined callbacks made with HTTP". They are usually triggered by some event happening in the source app. 

Nitech, you're familiar with HTTP-requests, right? It's kinda the way the web it built. A webhook is simply a POST request typically containing JSON, like this one, coming from your ERP-system: 

{
  "sku" : "JU40000365",
  "price" : "29999",
  "stock" : "9"
}


It says: Product with SKU JU40000365 has changes - and they're included in the JSON. 

The power of Webhooks is that they're triggered by the source app

Okay, I made that one up. But that's my understanding anyhow. The source detects a change - through whatever mechanism (event, polling, whatever), and triggers a webhook, if there is a webhook configured for that change. 

It's the way PayPal tells your shop that the purchase of order 123 was successfully paid - or declined. 

How to accept incoming webhooks

So, back to your question - atm. you have to create a plugin or module for Craft CMS in order to handle incoming Webhooks. 

If you have a look at Rias' Stripe Webhook Plugin for Craft, you can easily build your own plugin for your specific purpose. Look specifically at the controller. 

Also have a look at the Craft 3 documentation, How to build a plugin, which gives you what you need to scaffold and load a plugin into your Craft CMS repo.

I used pluginfactory.io to create a scaffold for the plugin. 

In finishing, you may ask why I can't simply just give you a zip-file with the finished plugin. My answer is that you'll be better off experimenting and learning this yourself.