# Invoke a payment with smart contract

I'm trying to create a function in my smart contract that will invoke a payment from the user, for example when a button is clicked metamask will ask to confirm the 0.10 ETH payment to my contract, I understand payable functions and have tested this in remix and can pay my contract but I want to know how to 'invoke' a payment with a predefined amount of Ether and request it from the user. Thanks

function userSendsEth() {

• Yes, I updated the above, it would still require the user initiating the transaction - not the contract though. But it would ensure that the user sent whatever amount you specify as someamount. – Karen S Jan 29 '18 at 1:30