How to resolve error: An unexpected 'StartArray' node was found when reading from the JSON reader. A 'StartObject' node was expected.?

I am trying to add an entity to Dynamics 2016 On Premise using the Web API. The Entity references three other entities. When I try to post the Entity, I receive the following error.

An unexpected 'StartArray' node was found when reading from the JSON reader. A 'StartObject' node was expected.

This error occurs on the three entities I am referencing: ccseq_clientid, ccseq_employeeid, ccseq_setid.

I have looked at this question and this question, but without success.

What does this error mean and how can I resolve it?

Variables

public contentType: string = "application/json;";
public dataType: string = "json";
public expenseTransaction: string = this.connection + "ccseq_expensetransactions";
public expenseTransactionSet: string = this.connection + "ccseq_expensetransactionsets";
public client: string = this.connection + "ccseq_clients";
public systemUser: string = this.connection + "systemusers";

Ajax Call

Create(expenses: Array<ExpenseTransactionBase>): void {
    for (let i: number = 0; i < expenses.length; i++) {
        $.ajax({
            url: this.expenseTransaction,
            type: "POST",
            contentType: this.contentType,
            accepts: this.contentType,
            dataType: this.dataType,
            data: JSON.stringify(expenses[i].toJSON()),
            success: function (data: any): void {
                alert("Success");
            },
            error: function (data: any) {
                alert("error");
            }
        });
    }
};

JSON Creation

toJSON(): any[] {
     let json = [];
     json[0] = {
         "ccseq_clientid@odata.bind": this.client + "(" + this.ccseq_clientid + ")",
         "ccseq_clientnumber": this.ccseq_clientnumber,
         "ccseq_employeefirstname": this.ccseq_employeefirstname,
         "ccseq_employeelastname": this.ccseq_employeelastname,
         "ccseq_employeeid@odata.bind": this.systemUser + "(" + this.ccseq_employeeid + ")",
         "ccseq_expenseerrorcode": this.ccseq_expenseerrorcode,
         "ccseq_generalledgername": this.ccseq_generalledgername,
         "ccseq_generalledgernumber": this.ccseq_generalledgernumber,
         "ccseq_groupcode": this.ccseq_groupcode,
         "ccseq_mastercardposteddate": this.ccseq_mastercardposteddate,
         "ccseq_mastercardtransactiondate": this.ccseq_mastercardtransactiondate,
         "ccseq_mastercardtransactionparentcompany": this.ccseq_mastercardtransactionparentcompany,
         "ccseq_navcompanycode": this.ccseq_navcompanycode,
         "ccseq_navemployeeid": this.ccseq_navemployeeid,
         "ccseq_navgeographycode": this.ccseq_navgeographycode,
         "ccseq_navjobclasscode": this.ccseq_navjobclasscode,
         "ccseq_navservicecode": this.ccseq_navservicecode,
         "ccseq_setid@odata.bind": this.expenseTransactionSet + "(" + this.ccseq_setid + ")",
         "ccseq_transactionamount": this.ccseq_transactionamount,
         "ccseq_transactiondate": this.ccseq_transactiondate,
         "ccseq_transactiondescription": this.ccseq_transactiondescription,
         "ccseq_transactiontype": this.ccseq_transactiontype,
         "ccseq_vendor": this.ccseq_vendor,
         "statecode": this.statecode
     };

     return json;
 }

As stated in the error, you should POST a JSON object, not an array.

I believe the change you need is to change:

toJSON(): any[] {
     let json = [];
     json[0] = {
         //...

to

toJSON(): any[] {
     let json = {
        //...