The Bancor Network operates on the main network for the Ethereum blockchain. Therefore, any third-party or Web3 wallet utilizing the Bancor Network must run on Ethereum's main network, and not on one of the test networks supported by Ethereum (e.g., Ropsten, Koven, Rinkeby).
If you see an error message that indicates you must switch to Ethereum's main network in order to perform transactions, this means your 3rd party external wallet service is currently set to run on one of the test networks supported by Ethereum. You will need to switch it to work on the main network in order to successfully perform transactions.