SNS subscribe HTTPS endpoint

I'm attempting to integrate a Google Chat webhook with the SNS https protocol but am having difficulty.

command1:

aws sns subscribe --topic-arn arn:aws:sns:us-east-1:123456789012:MyTopic --protocol https --notification-endpoint 'https://chat.googleapis.com/v1/spaces/AAAAaikfLEo/messages?key=<your-key>&token=<your-token>'

output:

{ "SubscriptionArn": "pending confirmation" }

Here are the cloud monitoring logs.

{ "notification": { "messageId": "0b72f18b-4267-4766-9196-58sckdsjwswf", "topicArn": "arn:aws:sns:us-east-1:123456789012:MyTopic", "timestamp": "2023-03-11 05:57:32.278" }, "delivery": { "deliveryId": "0b72f18b-4267-4766-9196-58sckdsjwswf", "destination": "https://chat.googleapis.com/v1/spaces/AAAAaikfLEo/messages?key=<your-key>&token=<your-token>", "providerResponse": "Bad Request", "dwellTimeMs": 62, "statusCode": 400 }, "status": "SUCCESS" }

I tried other commands as well, but they were ineffective.

command2:

aws sns subscribe
--topic-arn arn:aws:sns:us-east-1:123456789012:MyTopic
--protocol https
--notification-endpoint 'https://chat.googleapis.com/v1/spaces/AAAAaikfLEo/messages?key=<your-key>&token=<your-token>'
--attributes '{"http":{"defaultContentEncoding":"UTF-8","headers":{"Content-Type":"application/json"}}}'

error:

Parameter validation failed: Invalid type for parameter Attributes.http, value: OrderedDict([('defaultContentEncoding', 'UTF-8'), ('headers', OrderedDict([('Content-Type', 'application/json')]))]), type: <class 'collections.OrderedDict'>, valid types: <class 'str'>

not greeting the error in command1 but receiving no response However, the status code in the logs is 400, so I'm not sure what the error is; it could be about the header or something else.