Client-side, you can use the iotex-antenna@latestpackage. Below is an example of setting up WsSignerPlugin to connect to the wallet: it is nothing more than passing the plugin as a dependency when calling the Antenna object constructor.
Before sending the transfer or the contract call above, you need to open and unlock IoPay Desktop Wallet on the client machine. Once the wallet is ready and unlocked, you can run the script below in both the browser and the node environment, and then you can see the message to sign. Please click "Yes, sign transaction" in IoPay Wallet to continue and sign the message with the unlocked account.
This documentation portal is currently undergoing updates to align with the IoTeX 2.0 Whitepaper release. Information provided here may be incomplete, or out-of-date. Please use this portal for preliminary reference only, and check out the official IoTeX 2.0 Whitepaper for updated information.