Not aware of a maximum. The maximum might depend on the size of your environment and the way you handle the request and response. A large response could be split up in a receiving the data and mapping de data via the queue. I am not sure if you are publishing or consuming a rest-service but you might try to
If you’re dealing with rather large files, I would recommend building this outside of your core mendix application. A REST API is not really the best option when you’re dealing with large binary files.
You could instead integrate your Mendix app with AWS S3 or Azure blob storage. Those platforms support the upload of large files. You could then just authenticate your Mendix app with those platforms and perform the necessary work that way.