Can't serialize json inside json

[Horia22]

Should have been:
{"message":"{\"amount\":1.0,\"currency\":\"RON\",\"currency_code\":\"946\",\"unique_id\":\"44c860cc-14d8-4213-82cc-88b96998d273\"}"}

What I get:
{"message":"{"amount":5,"currency":"RON","currencyCode":"946","uniqueId":"73qyedhyecgyd7efyuaehudsjh"}"}