working with the refreshApex feature in LWC

Going by the documentation, it seems you will need to create an additional property and utilize that in your wired function.

To refresh a wired method, pass the argument the wired method receives (which is the wired value) to refreshApex(). In this sample code, the wired method is wiredGetActivityHistory(value). Hold on to the value provisioned by the wire service and pass it to refreshApex().

You will need to declare another variable, say mySendForSplitting and then utilize that in your sendForSplitting, something as:

sendForSplitting({error,data}) {
    this.mySendForSplitting = data;
    // rest of the code
}

And then use refreshApex() as below:

refreshApex(this.mySendForSplitting);

You can find an example on the lwc-recipe as well.