Parameters
- subscriptionPlanId
 - Specifies the subscription plan to match - pass 0 for all plans.
 - orderRange
 - Order number or range of orders to show.
 - userIdRange
 - User Id range of subscriptions to find.
 - firstName
 - The first name to match, by default a begins with match or use * wildcard to alter behavior.
 - lastName
 - The last name to match, by default a begins with match or use * wildcard to alter behavior.
 - The email name to match, by default a begins with match or use * wildcard to alter behavior.
 - expirationStart
 - Specifies to match subscriptions that expire on or after this date. Pass DateTime.MinValue for no start date.
 - expirationEnd
 - Specifies to match subscriptions that expire on or before this date. Pass DateTime.MaxValue for no end date.
 - active
 - If true only active subscriptions will be included in results
 - groupId
 - Given subscription group id
 - maximumRows
 - Maximum number of rows to retrieve
 - startRowIndex
 - Starting index from where to start retrieving
 - sortExpression
 - Sort expression to use for sorting the loaded objects
 
Return Value
A collection of subscriptions matching the given search criteria