Jira SDK: fetching Jira issues filtered by custom field

[Haitham Salem]

i have an issue while fetching Jira issues filtered by custom field, i am getting below error:

Response Content: {"errorMessages":["Error in the JQL Query: Expecting a field name but got ')'. You must surround ')' in quotation marks to use it as a field name. (line 1, character 22)"],"errors":{}}

the code is: 

var issues = jiraRestClient.Issues.Queryable.Where(x => x.Project == ConfigrationManager.JiraProject
&& x.CustomFields["Transaction Type / ATM Number"].Values[0] == "Deposit");

The custom field "Transaction Type / ATM Number" is cascaded drop down list it has two elements in value string array, see below picture

please help