JSON解码失败的原因是您提供的JSON是无效的JSON。您需要正确地在键和值周围提供引号，并且在JSON内容中也有一些转义字符，我将在下面强调。
如果转义字符应该在那里，最终的JSON应该看起来像这样;

[{key: "persist:auth-cred", value: {"user":"{\"image\":[\"public/images/branch/1664746288495-65170.jpg\",\"public/images/branch/1664747603436-15997.jpg\"],\"holiday\":\"0\",\"country\":\"India\",\"business_segment\":[{\"value\":\"ab3af5ec-b83a-4918-9be3-d7ac98e24c1f\",\"label\":\"Salons\"},{\"value\":\"1b1def14-3fa2-4799-b118-ce83b66ab72d\",\"label\":\"Skin Care Clinics\"}],\"taxSlab\":18,\"avg_rating\":4.9,\"isActive\":true,\"_id\":\"633a03310705114b4e232c9e\",\"name\":\"The Vega Salon\",\"phone\":\"7062559946\",\"email\":\"[email protected]\",\"password\":\"$2b$10$p8h6VLgZEjKrE9u8J8UFl.s8JdE0Wghpw/Z4ajcqe8JP.8fQxzci.\",\"gender\":\"unisex\",\"address_line1\":\"Rose Street\",\"address_line2\":\"Malviya Nagar\",\"city\":\"Jaipur\",\"zipcode\":\"302011\",\"website\":\"\",\"gmap\":\"SDC Building, 38-39, Pradhan Marg, Mauji Colony, Moji Nagar, Malviya Nagar, Jaipur, Rajasthan 302017, India\",\"description\":\"Perfect salon for both men and women. Making the best day of your life the most memorable one is a promise extended by us. Our dedicated staff understands the importance of readying you to look your best on your big day. Ensuring the perfect look that compliments both your attire and the wedding theme offering you the best bridal & groom makeup package is our specialty. Whether you want to sport the classic chic look or a vintage boho, we ensure you look pretty n picture perfect and at the centre of everyone’s world.\",\"startTime\":\"2022-10-03T04:30:00.000Z\",\"endTime\":\"2022-10-03T16:30:00.000Z\",\"taxNo\":\"08AARHF1382D1S5\",\"latitude\":26.8592831,\"longitude\":75.80840859999999,\"logo\":\"public/images/branch/1669967198797-79350.jpg\",\"state\":\"NA\",\"countryCode\":91,\"uuid\":\"957672ff-51f7-4528-96ed-84df0ef724d9\",\"businessUuid\":\"949001e9-5ae1-488d-9115-d9405b8021ed\",\"__v\":0,\"otherContact\":\"\",\"id\":\"633a03310705114b4e232c9e\",\"businessCalenderType\":\"shift\"}","authenticated":"true","token":"\"eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpZCI6IjYzM2EwMzMxMDcwNTExNGI0ZTIzMmM5ZSIsImlhdCI6MTY5NzYxMTk3OSwiZXhwIjoxNzAwMjAzOTc5fQ.sDsVKyoODAtl6LLqnLyWcJ6x9VwskXsQGcPIq-Vq6fU\"","role":"\"branch\"","_persist":"{\"version\":-1,\"rehydrated\":true}"}}]

否则你的JSON应该看起来像这样才是真正可接受的JSON格式;

[{"key":"persist:auth-cred","value":{"user":{"image":["public/images/branch/1664746288495-65170.jpg","public/images/branch/1664747603436-15997.jpg"],"holiday":"0","country":"India","business_segment":[{"value":"ab3af5ec-b83a-4918-9be3-d7ac98e24c1f","label":"Salons"},{"value":"1b1def14-3fa2-4799-b118-ce83b66ab72d","label":"Skin Care Clinics"}],"taxSlab":18,"avg_rating":4.9,"isActive":true,"_id":"633a03310705114b4e232c9e","name":"The Vega Salon","phone":"7062559946","email":"[email protected]","password":"$2b$10$p8h6VLgZEjKrE9u8J8UFl.s8JdE0Wghpw/Z4ajcqe8JP.8fQxzci.","gender":"unisex","address_line1":"Rose Street","address_line2":"Malviya Nagar","city":"Jaipur","zipcode":"302011","website":"","gmap":"SDC Building, 38-39, Pradhan Marg, Mauji Colony, Moji Nagar, Malviya Nagar, Jaipur, Rajasthan 302017, India","description":"Perfect salon for both men and women. Making the best day of your life the most memorable one is a promise extended by us. Our dedicated staff understands the importance of readying you to look your best on your big day. Ensuring the perfect look that compliments both your attire and the wedding theme offering you the best bridal & groom makeup package is our specialty. Whether you want to sport the classic chic look or a vintage boho, we ensure you look pretty n picture perfect and at the centre of everyone’s world.","startTime":"2022-10-03T04:30:00.000Z","endTime":"2022-10-03T16:30:00.000Z","taxNo":"08AARHF1382D1S5","latitude":26.8592831,"longitude":75.80840859999999,"logo":"public/images/branch/1669967198797-79350.jpg","state":"NA","countryCode":91,"uuid":"957672ff-51f7-4528-96ed-84df0ef724d9","businessUuid":"949001e9-5ae1-488d-9115-d9405b8021ed","__v":0,"otherContact":"","id":"633a03310705114b4e232c9e","businessCalenderType":"shift"},"authenticated":true,"token":"eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpZCI6IjYzM2EwMzMx10adfadfad0e5b11f"}}]

关键注解是;

• [{“key”：persist：auth-cred，已更改为[{“key”：“persist：auth-cred”，-这在键周围提供了有效的引号。
• 转义字符（\”）也被更改为引号，以确保它们有效。

首先，您需要将value数据转换为String，并在字符串字面量前面放置r。
这就像：

var valueData = r"""{"user":"{\"image\":[\"public/images/branch/1664746288495-65170.jpg\",\"public/images/branch/1664747603436-15997.jpg\"],\"holiday\":\"0\",\"country\":\"India\",\"business_segment\":[{\"value\":\"ab3af5ec-b83a-4918-9be3-d7ac98e24c1f\",\"label\":\"Salons\"},{\"value\":\"1b1def14-3fa2-4799-b118-ce83b66ab72d\",\"label\":\"Skin Care Clinics\"}],\"taxSlab\":18,\"avg_rating\":4.9,\"isActive\":true,\"_id\":\"633a03310705114b4e232c9e\",\"name\":\"The Vega Salon\",\"phone\":\"7062559946\",\"email\":\"[email protected]\",\"password\":\"p8h6VLgZEjKrE9u8J8UFl.s8JdE0Wghpw/Z4ajcqe8JP.8fQxzci.\",\"gender\":\"unisex\",\"address_line1\":\"Rose Street\",\"address_line2\":\"Malviya Nagar\",\"city\":\"Jaipur\",\"zipcode\":\"302011\",\"website\":\"\",\"gmap\":\"SDC Building, 38-39, Pradhan Marg, Mauji Colony, Moji Nagar, Malviya Nagar, Jaipur, Rajasthan 302017, India\",\"description\":\"Perfect salon for both men and women. Making the best day of your life the most memorable one is a promise extended by us. Our dedicated staff understands the importance of readying you to look your best on your big day. Ensuring the perfect look that compliments both your attire and the wedding theme offering you the best bridal & groom makeup package is our specialty. Whether you want to sport the classic chic look or a vintage boho, we ensure you look pretty n picture perfect and at the centre of everyone’s world.\",\"startTime\":\"2022-10-03T04:30:00.000Z\",\"endTime\":\"2022-10-03T16:30:00.000Z\",\"taxNo\":\"08AARHF1382D1S5\",\"latitude\":26.8592831,\"longitude\":75.80840859999999,\"logo\":\"public/images/branch/1669967198797-79350.jpg\",\"state\":\"NA\",\"countryCode\":91,\"uuid\":\"957672ff-51f7-4528-96ed-84df0ef724d9\",\"businessUuid\":\"949001e9-5ae1-488d-9115-d9405b8021ed\",\"__v\":0,\"otherContact\":\"\",\"id\":\"633a03310705114b4e232c9e\",\"businessCalenderType\":\"shift\"}","authenticated": "true","token":"\"eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpZCI6IjYzM2EwMzMxMDcwNTExNGI0ZTIzMmM5ZSIsImlhdCI6MTY5NzYxMTk3OSwiZXhwIjoxNzAwMjAzOTc5fQ.sDsVKyoODAtl6LLqnLyWcJ6x9VwskXsQGcPIq-Vq6fU\"","role": "\"branch\"","_persist": "{\"version\":-1,\"rehydrated\":true}"}""";

OR

var valueData = r'' + YourObject.value.toString();

OR

var valueData = r'' + YourObject['value'].toString();

之后，解码数据，如：

var decodedData = json.decode(valueData);
print(decodedData['user']);

// You can show the decodedData['user'] consol log like below : 
{"image":["public/images/branch/1664...

然后，再次解码数据如下所示，以获得ex的其他参数：image：

var data = json.decode(decodedData['user']);
print(data['image'].first);

// You can show the data['image'].first consol log like below :
public/images/branch/1664746288495-65170.jpg

我希望这个解决方案可以为您工作。