Fatal Error Allowed Memory Size of 134217728 Bytes Exhausted CodeIgniter XML-RPC

Question

My client point of sale (POS) systems send updated sales data to a central database on a regular basis, where it is collected and stored in order to generate reports.

The client POS is built on PHPPOS, and I've developed a module that sends sales information to the service using the common XML-RPC library. The webservice component of the server system is constructed using CodeIgniter and employs the XML-RPC and XML-RPCS libraries. I see the following issue whenever I send a large amount of sales data (as few as 50 rows from the sales database and individual rows from sales items referring to each item inside the sale):

Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 54 bytes)

The default setting in php.ini is 128M, but I imagine that's a big quantity to mess up. In fact, I tried increasing this amount to 1024M, but all that happened was that it took longer for the error to occur.

In terms of actions I've done, I've tried turning off all server-side processing and configured it to always provide a pre-written response. However, I think the issue is with how the data is really sent. Even after I disabled PHP's maximum script execution time, there were still issues.