First off, I'm not sure if this is the right section to post this or not. I looked at the Extension Development section but decided my issue wasn't a proper fit there. Apologies for any confusion.
I'm currently building an Android app which interfaces with a specific installation of PHPBB 3.1 and allows the user to perform limited actions within that board. Notably viewing/sending private messages and retrieving posts from a specific thread. This is achieved using Volley and simply requesting and receiving HTML from the server as one would from a browser, so I'm not directly touching the database or backend in any way that a normal user would not, in theory at least.
Currently all of the desired core features work except sending private messages. Using the broswer's network tab, I deconstructed the "Compose" page and figured out what parameters and such needed to be sent in with the form. Currently I request the Compose page and extract the Sid. Then I use the add function to retrieve the desired user's id for sending the message. After retrieving this and the new Sid, I build a POST request to try and send the message. I set all of the parameters that I can see in Firefox. The problem is, while the message sends normally in the browser, it does not send from the app. Instead the response page is just my Inbox page. No error mesages of any sort are displayed. I tried tracking down the logic for this in PHPBB's includes/ucp/ucp_pm_compose.php file, but I couldnt see a place where it redirected to the inbox directly from the submit button. Help figuring out what is causing this would be greatly appreciated
Let me know if anything needs further clarification.
Also, I asked the board manager and he said the only modification installed that in any way affects the behavior of PMs is the PM Search mod, version 1.03.