I'd really appreciate if someone can help with this error: Failed to process webhook: Error: Could n

I’ve been stuck on this issue for a while now. If anyone can help or direct me to the right point of contact, I’d be grateful.

When I run my app using shopifyApp from shopify/shopify-app-express, it keeps giving:

Failed to process webhook: Error: Could not validate request HMAC

My hostname:

hostName: 'localhost:4321',

I am following the documentation to the point but it isn’t clear and I cannot find the problem. Please, can anyone advise?