This is probably a very simple problem to solve, but I am setting up a node.js backend using express for my Dapp and I can now deploy new contracts just fine.

I now need to figure out how to make calls to a function in an existing contract (created previously in Remix). I have the following syntax:

    const platformArtifacts = require('./build/contracts/Platform.json');
    var myPlatformContract = contract(platformArtifacts);
    myPlatformContract.setProvider(provider);

I know that this is wrong, but I do not know how to do it properly. The function call I make is:

	var insurerAddress = '0x...';
	var myClientUIC = req.body.clientUIC;
	var myClientName = req.body.clientName;
	var myClientGroup = req.body.clientGroup;
	var myClientNACE = req.body.clientNACE;
	var myCreditLine = req.body.creditLine;
	var myCreditLineDate = req.body.creditLineDate;
	var myClientCurrency = req.body.clientCurrency;
	var myClientCity = req.body.clientCity;
	var myClientCountry = req.body.clientCountry;

	myPlatformContract.at("0x...").createClient(myClientUIC, myClientName, myClientGroup, 
		myClientNACE, insurerAddress, myCreditLine, myCreditLineDate, myClientCurrency, myClientCity, myClientCountry,
		{ from:provider.getAddress() })
        .once('transactionHash', function(hash) {
            console.log("TxHash: " + hash);
        }).on('receipt', function(receipt) { console.log("receipt: " + JSON.stringify(receipt)); })
			.then(function(result) {
        }, function(error) {
            console.log(error);
        });

The error I get is:

    TypeError: myPlatformContract.at(...).createClient is not a function

However, createClient is a function. I would appreciate any help you an give me with this beginner's issue! Many thanks. Phil