Not getting metamask prompt when interacting with smart contract when provider is JsonRPC

[redigaffi]

Hello,

User gets asked for approval in metamask when used this provider when calling a smart contract
new ethers.providers.Web3Provider(window.ethereum);

But, I dont get that behaviour when using JSON RPC Provider like this:
new ethers.providers.JsonRpcProvider("http://127.0.0.1:7545");

My idea is basically to enforce usage of certain chains, e.g, I want to force that JSON RPC because I want users to use the BSC only, if my approach to do this is incorrect, how can I enforce BSC networks only?

[ricmoo]

The MetaMask operates as an EIP-1193 provider. You cannot connect to a local socket on a users machine (which is what 127.0.0.1 refers to).

You must use MetaMask (window.Ethereum) if you want to access MetaMask itself.

I believe you can specify the chain ID if you wish, to individual methods and you should check the chain ID of the provider to make sure it matches.

But localhost is not going to work for most users. Does that make sense?

[redigaffi]

Yea, localhost was just for testing purpose, (using Ganache locally), in prod I would use Binance RPC. So, if I understand correctly, my only bet would be to check the chain id? provider.getNetwork()... ? I was expecting this answer

Another question maybe a little bit offtopic... Not 100% sure how that chain ID works, could it happen that 2 different blockchains have the same chain id? is that chain id attribute only for eth forks?

[redigaffi]

Also, when im on a site that requires X network, and im on another, a metamak popups asks you to change your network, how do you do that with ethers.js?