PureEngage On-Premises

I've written a statement to perform RequestSingleStepTransfer in the code like this:
RequestSingleStepTransfer reqBlindTransfer = RequestSingleStepTransfer.Create(thisDN, connID, transferRoutePt, "", null, null, null);

But it returned "Unsupported operation" error.

The messages generated when debugging:
'RequestSingleStepTransfer' ('25')
message attributes:
AttributeThisDN [str] = "6154"
AttributeConnID [long] = 006D02674398B7DD
AttributeOtherDN [str] = "2732"
AttributeLocation [str] = ""
AttributeReferenceID [int] = 5

'EventError' ('52')
message attributes:
AttributeEventSequenceNumber [long] = 286133
AttributeCustomerID [str] = "Resources"
Time            = ComplexClass(TimeStamp):
 AttributeTimeinuSecs [int] = 14000
 AttributeTimeinSecs [int] = 1437967615
AttributeErrorCode [int] = 51
AttributeCallID [int] = 12523
AttributeConnID [long] = 006D02674398B7DD
AttributeThisDN [str] = "6154"
AttributeReferenceID [int] = 5

Which type of PBX do you using? If any specific (like Alcatel, Avaya, etc.) check with PBX expert if the PBX allows it

Check with your T-Server Deployment guide. There's a table in every guide showing the Supported T-Library Functionality. Your feature request is called "TSingleStepTransfer" and is not supported by T-Server for Avaya Communication Manager for example.

Please keep in mind that the single step transfer is also not supported in some Infomart reporting call scenarios. Business wise speaking, it is usually considered a bad practice, since the customer which is on hold will be passed directly to another customer service representative without him being introduced to the target agent.