How to extract value from serialized json response in Jmeter

I am getting a response in form of serialized json format for an api request as below

{"Data":"{\"orderId\":null,\"Tokens\":{\"Key\":\"abcdefgh123456\",\"Txnid\":\"test_5950\"}","success":true,"Test":"success"}

I want to extract Key value in Jmeter and I have to use into next request. Can someone help me on extracting the value?

If your JSON really looks exactly like you posted the most suitable Post-Processor would be Regular Expression Extractor

The relevant regular expression would be something like:

"Key"?\s*:?\s*"(\w+)"

where:

• ``?\s*` - arbitrary number of whitespaces (just in case)
• \w - matches "word" character (alphanumeric plus underscores)
• + - repetition
• () - grouping

More information:

• Using RegEx (Regular Expression Extractor) with JMeter
• Perl 5 Regex Cheat sheet
• JMeter: Regular Expressions