Add custom field to Jira search query using .NET NuGet package

[Deleted user]

I am using the Atlassian.Jira NuGet package in my web app. 

I can successfully query Jira using built in fields for example Project, ResolutionDate etc. but I cannot use a custom field.

I have a custom field named "Organizations"  and I want to add this to my query where it is equal to a certain string.

Here is my query:

var issues = from i in jira.Issues.Queryable
where i.Created >= dateFrom &&
i.Created <= dateTo && i.Type != "Change" && i["Organizations"] == organization
select i;

I have tried the following:

i["Organizations"] == organization

Returns 400. Operator ~ not supported.

i["Organizations"].ToString == organization

 Returns Index was out of range. Must be non-negative and less than the size of the collection. 

Sounds like there is nothing to return but I can see issues in the portal.

I also tried 

i.CustomFields["Organizations"].Values[0] == organization

400. 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

Though I don't think it is supposed to be used this way.

Any help is appreciated.