For technical reasons that I doubt are interesting, there is a connector ledge on the socket bands, that sometimes requires a bit of a push, but all BA's headphone sockets now have 3.5mm sockets, compatible with almost all wired headphone and I doubt that Ms. PG is waltzing around with a 6.35mm headphones. The adapter shown in the Amazon link obviously won't work on BA. If you only had one channel, it means that the jack connectors only made connection with the first band of the socket (and the wrong one in terms of left verus right); alternatively there can be a fault on the connectors, usually in the socket (some kid stuffing things in them) that weakens the connector band contact. This can be fixed by cleaning out the socket with a suitable pin (carefully) or by twisting the jack a few degrees round.

I think this is on a 787 but it's pretty much the same everywhere in CW. This shows my 3.5mm headphone jack, the other socket for Noise Reduction.