I have a `fileupload` field on a custom module that I need to replace the file for but I don't know how to get the ZFS ID from the module record.

# Getting the current fileupload

1. GET https://www.zohoapis.eu/crm/v7/<MODULE>/<ID>
   
   # Response
   {
     data: [{
      // fileupload field
       Invoice_PDF: [{
            id: <REDACTED>, // Numeric ID. Probably the ID of the linking module record
            File_Id__s: <REDACTED>, // This is not the ZFS ID. It also contains both numbers and letters but is way shorter
   
2.         Created_Time__s: '2024-12-13T11:55:11+01:00',
3.         File_Name__s: '2022-12-01-Easyfairs-Supercube-01.jpeg',
4.         Modified_Time__s: '2024-12-13T11:55:11+01:00',
5.         Created_By__s: <REDACTED>,
6.         Size__s: 3323506,
7.         id: '11191000117833056',
8.         Owner__s: <REDACTED>,
9.         Modified_By__s: <REDACTED>,
    }]
  }]
}

# Trying to replace the fileupload values

1. POST https://www.zohoapis.eu/crm/v7/<MODULE>/<ID>
   
   # Body contents
   {
     data: [{
       // fileupload field
       Invoice_PDF: [
           { File_Id__s: myFile.zohoFS_ID },
           { id: myZohoModuleRecord.data.Invoice_PDF[0].id, _delete: null }, // Delete the previous link entry
       ]
     }]
   }
   
   // This API call errors when I'm doing a delink + link for the same Zoho file.

In short: I have no way of knowing if the file is already linked, based on the data that Zoho gives me.
When handling files I have to handle these scenarios:
 - Module record has no `Invoice_PDF` linked to it => POST /files and PUT /<MODULE>/<ID> // This works
 - Module record has `Invoice_PDF` linked to it
  - Is it the same PDF? Idk?
  - Is it another? Why do the IDs in `File_Id__s` differ between POST /files and GET /<MODULE>/<ID>?