Saving Related Line Items

public void saveRelatedLineItems(String cartId, String lineItemId) {

		// Prepare the request structure to be passed to the API
		Apttus_Config2.CPQStruct.SaveRelatedLineItemRequestDO requestDO = new Apttus_Config2.CPQStruct.SaveRelatedLineItemRequestDO();
		requestDO.CartId = cartId;

		List<Apttus_Config2__RelatedLineItem__c> relatedLineItemSOs = [SELECT Apttus_Config2__LineItemId__c, Apttus_Config2__WeightageType__c, Apttus_Config2__WeightageAmount__c FROM Apttus_Config2__RelatedLineItem__c WHERE Apttus_Config2__LineItemId__c =: lineItemId];

		// below is simple example logic to set the Weightage Amount and setting Weightage type to Amount
		// Customers can have their use cases implemented here
		for (Apttus_Config2__RelatedLineItem__c relatedLineItemSO : relatedLineItemSOs) {
			relatedLineItemSO.Apttus_Config2__WeightageType__c = 'Amount';
			relatedLineItemSO.Apttus_Config2__WeightageAmount__c = 35;
			Apttus_Config2.CPQStruct.RelatedLineItemColl relatedLineItemDO = new Apttus_Config2.CPQStruct.RelatedLineItemColl();
			relatedLineItemDO.RelatedLineItemSO = relatedLineItemSO;

			requestDO.RelatedLineItems.add(relatedLineItemDO);
		}

		// Invoke the API by passing the request formed above
		Apttus_Config2.CPQStruct.SaveRelatedLineItemResponseDO responseDO = Apttus_Config2.CPQWebService.saveRelatedLineItems(requestDO);

		// Check the response for errors if any
		if (!responseDO.IsSuccess) {
			System.debug('Errors thrown :');
			if (responseDO.Errors != null && responseDO.Errors.size() > 0) {
				for (String strError : responseDO.Errors) {
					System.debug('\nError - ' + strError);
				}
			}
		}
}