Custom workflow with Currency Fields

CRM 2016 On premisis

I am trying to write a workflow that imports data from a legacy SQL server. Currently the only sticking point I have is on one field

SQL field is type Money

CRM Field (new_transactionvalue) is type currency

I have chopped out all the other code due to security. The data is retrieved from SQL via a stored procedure and the workflow reads the results and inserts the records to CRM

  Dim NewTransaction As New Entity("new_transactions")
                        NewTransaction("new_transactionvalue") = SQLReader.GetValue(TransValue)
                        service.Create(NewTransaction)

Whilst the rest of the crm fields are being populated, new_transactionsvalue is not being populated. When accessing a record through CRM, if I try and manually put a value in the transactionvalue field, I get a red cross with a message 'a currency is required if a value exists in a money field. Select a currency and try again.'

I am at a loss how to overcome this. Any suggestions please