The smart account (sender) has been previously set up. You might be attempting to initialize the account more than once.

​
Potential Fix

Eliminate the initCode from the user operation: 
const operationHash = await bundler.submitUserOp({
    // Remove this line
    // initCode: "0xd74a8b63df73223fcc89f604d6738e66719dbc...",
    // Add this line instead
    initCode: "0x",
    // Other user operation details...
})