Json deserialize issue in service class An exception occured when invoking the operation – Type ‘Class’ is not supported by serializer. D365 Finance and operations

Yesterday, I was working on integration, and everything was going fine. However, when I tried to retrieve a string from the DataContract, it threw an error: “Type ‘Class’ is not supported by the serializer.” The issue persisted even when I used Newtonsoft. The rest of the logic was functioning correctly.

Eventually, I discovered that the issue was due to missing AX 2012 attributes on the list’s getter/setter or parameter. Once I added those attributes, the actual getter/setter started working as expected.

 [
    DataMemberAttribute('transactions'),  
    DataCollectionAttribute(Types::Class, classStr(DSTTransactionDC))  
  ]  
  public List Parmtransactions(List _transactions = transactions)  
  {  
    transactions = _transactions;  
return transactions;
  }

I have to add following

  AifCollectionTypeAttribute('_transactions', Types::Class, classStr(DSTTransactionDC)),
  AifCollectionTypeAttribute('return', Types::Class, classStr(DSTTransactionDC))

After that getter setter become something similar

 [
    DataMemberAttribute('transactions'),  
    DataCollectionAttribute(Types::Class, classStr(DSTTransactionDC)),  
    AifCollectionTypeAttribute('_transactions', Types::Class, classStr(DSTTransactionDC)),  
    AifCollectionTypeAttribute('return', Types::Class, classStr(DSTTransactionDC))  
  ]  
  public List Parmtransactions(List _transactions = transactions)  
  {  
    transactions = _transactions;  
 return transactions;
  }

after this change, datacontract easily serialise. 
Also change attribute at class header from datacontracattribute to dataContract.

Hope you like this post.