S3 Copy Issue – Calling the UploadPartCopy operation: Cannot access through this access point

I’m trying to copy data from our data provider, but I’m getting the error “UploadPartCopy operation: Cannot access through this access point”. I’m not sure if there’s any issues with the IAM policy I’ve setup?

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "AllowDecryptS3Object",
            "Effect": "Allow",
            "Action": [
                "kms:Decrypt"
            ],
            "Resource": "*"
        },
        {
            "Sid": "AllowGet",
            "Effect": "Allow",
            "Action": [
                "s3:*"
            ],
            "Resource": "*",
            "Condition": {
                "StringEquals": {
                    "s3:DataAccessPointArn": "[data provider's access point arn]"
                }
            }
        },
        {
            "Sid": "S3SaveBucket",
            "Effect": "Allow",
            "Action": [
                "s3:*"
            ],
            "Resource": [
                "arn:aws:s3:::my_bucket_placeholder",
                "arn:aws:s3:::my_bucket_placeholder/*"
            ]
        }
    ]
}