generate_presigned_post presigned url upload is failing with invalid policy condition if key contains $$

[asvashrith]

Below code is generating a presigned url but when we are trying to upload the file it is failing with error Accessdenied: Invalid policy condition(refer below for detailed error message). If we remove $$ symbol it is working we are able to upload the file

s3_client = boto3.client('s3',api_version='2006-03-01',config=boto3.session.Config(signature_version='v4'))
response = s3_client.generate_presigned_post(
        Bucket="sample_bucket",
        Key="Folder/filename$$.txt",
        Conditions=conditions,
        Fields=fields,
        ExpiresIn=url_exp_time,
    )

AccessDeniedInvalid according to Policy: Policy Condition failed: ["eq", "$key", "Non-Attest/Engagement/Deloitte Audit/2025/R#4ce6a258-45f7-4ebf-84be-a8879e02e97f_Roll Over Doc 1_20267$$_Annual - Copy.csv"]F72R27WZG85A7F0YQWKnrDXfFDoBcci1coj8mbJGxLOIO2j0EHamAsaU4o55U9thfYVSYZOjIQ1U9jobYrE64yjZWW0uxvwRx52KoQ==

We expect the file upload to work even if the key contains $$ or any other special characters, if there are any restrictions to the characters in key please provide documentation or refernce