Yes, @Ahmad_Anwar – the issue is that you’re creating a custom app in your partner organization and attempting to deploy it to a merchant’s store. Unfortunately that won’t work.
If you’re building this for external merchants (not your own store), client credentials won’t work for you. You’d need to use the authorization code grant flow or token exchange instead, which involves an OAuth redirect to get merchant approval.
There’s a comprehensive thread here that walks through this entire transition: How to use Shopify’s API with custom app changes?