Here’s a look at what each parameter is and what it does. You may need to copy/paste this into a text editor and print it to get a better look.

{
    "fm":{
        "container": {
            "field": "(required, string) The name of the targeted container field",
            "key": {
                    "field": "(required, string) The name of the field which stores the container field record's primary key",
                    "value": "(required, string) The value of the primary key for the targeted record" },
            "layout": "(required, string) The name a the targeted layout (container must be visible on layout)" },
        "database": {
            "auth": "(optional, string) A base64 encoded username and password of a filemaker account with fmrest enabled",
            "name": "(required, string) The name of the targeted FileMaker database" },
        "FQDN": "(required, string) The FQDN of the targeted FileMaker server",
        "return": {
            "log": {
                "field": "(optional, string) the name of a text field where log data will be written",
                "layout": "(optional, string) the name of a layout where a log record can be created once the upload is completed" },
            "url": {
                "key": {
                    "field": "(optional, string) the name of the field which stores the primary key for the alternate record",
                    "value": "(optional, string) the value of the primary key for the alternate record (default: container field's record)" },
                "layout": "(optional, string) an alternate layout to store the uploaded URL address (default: container field's layout)" ,
                "field": "(optional, string) The name of the field on the container's layout where the uploaded URL address should be stored" }},
        "script": {
            "layout": "(optional, string) The layout from which to run the targeted FileMaker script (default: container field's layout)",
            "name": "(optional, string) The name of a FileMaker script to perform in the targeted database once the upload is completed (default: null)",
            "parameter": "(optional, string) The parameter for the targeted FileMaker script (default: empty)" }},

    "s3": {
        "bucket": "(required, string) the targeted s3 bucket",
        "key": "(required, string) the full name of the file as it should appear in s3, including any prefixes",
        "makePublic": "(required, boolean) set to true if the uploaded file should have a public URL",
        "region": "(optional, string) the AWS region of the bucket (example: us-east-1)" }
}