APIs - what is the file upload limit for pdfs ?

I have created a function that uploads pdf documents from a url so that I can effectively move from an old system to Zoho. I read on this page :
https://www.zoho.com/creator/help/api/v2/upload-file.html

The image and signature fields can accept an image that doesn't exceed 10 MB
The file upload, audio, and video fields can accept a file that doesn't exceed 50 MB

However when using invoke to upload pdfs to a file field I get the error that the limit is 5242880 bytes which is approx 5.24mb (i know it's not exact). I can use invoke to get the file size of each file using getFileSize() and the ones that are failing are all under 20MB.

What's the correct limit ?

This is the function code I am using

void UploadFromExtURL()
{
for each varRecord in Contracts[contract_size_check = false]
{
//Get the contents of each url saved in the contract_url_link (text) field
varURL = varRecord.contract_url_link;
varGetExtURL = invokeurl
[
url :varURL
type :GET
];
//Get the file size of the link
varFileSize = varGetExtURL.getFileSize();
//
//Find the existing record and update the file size and upload file
varFindExisting = Contracts[contract_url_link = varURL];
varFindExisting.contract_file_size=varFileSize;
varFindExisting.contract_signed_file=varGetExtURL;
}
}