A quick google search shows that you are likely not passing JSON into the deserialize object method.
c# - Unexpected character encountered while parsing value - Stack Overflow[
^]
Given you didn't provide much of a code sample, I'm going to say that response.Content isn't actually a string and is where you issue is coming in.
You need to ensure that response.Content is a string and not a HttpResponseMessage.
Also, if response.Content is how I think it is being used. You probably need to use it with the ReadAsString method in order to get it into a string format for Deserialization.