Using Variables_CreateOrUpdateVariableDeclaration with the JSON api

I am trying to create Free Text variables with the Json api.

Here is the JSON I am posting to Variables_CreateOrUpdateVariableDeclaration:

{
"API_Key":"apikey1",
"teamcity_build":"my_variable_name",
"Scope_Code":"X",
"Scoped_Application_Id":14,
"Scoped_Environment_Id":3,
"Required_Indicator":"Y",
"Variable_Configuration":"<Inedo.BuildMaster.Extensibility.Variables.FreeTextVariable Assembly="BuildMasterExtensions"><Properties /></Inedo.BuildMaster.Extensibility.Variables.FreeTextVariable>",
"Sensitive_Indicator":"N"}

Here is the response I get:

9413161Variables_CreateOrUpdateVariableDeclaration24`XML parsing: line 1, character 70, A string literal was expected

Can you please help me resolve the issue?

Product: BuildMaster
Version: 4.5.2

I would also like to note, I am using C# and the issue appears to come from the quotes around Assembly name. I am unsure how else to send it as I have to escape the double quotes on my side. So if you could get a C# sample that creates a variable declaration that would be much appreciated. Thank you.

Using a \ character is correct for escaping in JSON; that should work. We will try to reproduce this, but in the meantime are you able to use single quotes instead in the XML?

Assembly='BuildMasterExtensions'

should also parse as valid XML if I'm not mistaken.