You have likely experienced an old problem. Apple 3.5mm audio ports are quite precise; the 3.5mm plugs on external devices—not so much.
Deep in the port is a mute switch that turns off the built-in speakers when the port is in use. Some plugs are not built to tight specs and, If their tip is too long, it can jam the mute switch if the plug is inserted "to the hilt."
The quality of the external device does not seem to be a factor. I have cheap "no-name" external speakers whose plug never caused a problem. On the other hand, I have a quality set of headphones whose plug must be seated like this to avoid a jammed mute switch:
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On older Mac computers, you could look in the port and see a red glow if the mute switch were jammed. As I've never jammed the port on any of the four or five iPads we've owned, I do not know it this is still a "feature."
The iPad was not designed to be opened; even an Apple store will have to send it to one of their centralized repair centers for service, and that usual means they replace the iPad in-kind at a considerable cost if you don't have APpleCare+, rather than taking time to repair yours. This is the cost from Apple's own repair estimator:
So, first try this:
— Turn off the iPad.
— insert a standard 3.5mm audio plug into the port
— GENTLY apply a little pressure to the plug at positions of 0°, 90°, 180° and 270°.
— At each position, give the plug a very GENTLE "wiggle,"
Many times that will release a jammed mute switch without resorting to tools or service.
