Please set the option ":quirks_mode => true" when calling JSON.parse in
pact/consumer/mock_service/rack_request_helper.rb, line 31.
Ruby JSON library doesn't consider serialized string as a correct JSON value (which is is false statement!) and this quirks_mode is needed for working with string encoded as JSON:
https://makandracards.com/makandra/15611-how-to-fix-unexpected-token-error-for-json-parse