I do not know what you use to "process a request from the app server"?

1. Do you have Long String support turned on in, System > Configuration > Memory and Startup?

2. If you are using webservices you can modify the generated classes and change payload to type %GlobalCharacterStream

https://cedocs.intersystems.com/latest/csp/docbook/DocBook.UI.Page.cls?KEY=GSOAP_webclients#GSOAP_clie%20nt_the_long_string_problem