RS232 interfacing can be difficult.
Make sure you know the RX and TX pins on your connectors. Use a scope, check it, and confirm baud rates. Ideally have code that can send a continuous stream of characters. 'U' being a particularly good pattern.
Know your cables, understand the connectors on both ends, if the cable is straight-through, or cross-over. Understand if your gender-changer or null-modem adapters is straight-through, or cross-over.
Check if you need flow control (CTS/RTS or DTR/DSR) at either end.
In the late 80's we had a device called an Interfaker that allow signals to be probed and patched, because every manufacturer had their own connectors, quirks, and implementations of serial interfaces.
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