I can’t get my AUX cable to work... any one got any ideas?

I have a 2006 3.0D E53 with Business Radio with Audio Cassette tape player and CD 6x stack in the trunk. I have bought the 65 12 0 153 502 adaptor cable and have done the install, all as per instructions, but I just do not get the AUX mode when I scroll through the modes available.

I have checked all the pin numbers and sockets etc., multiple times, and everything is correct.

I have done a battery disconnect, to no avail.

I have checked the AUX cable and it has the correct 300KΩ resistance between the left and right audio.

Most of the articles I have read here mention this AUX install on the Business Radio with CD and/or Nav, but they don’t seem to mention those with Audi Cassette players, so I don’t know if this is my problem?

If anyone knows please can you tell me if this Radio is not compatible, or if there is anything else I can try? The label on the Business Radio is as follows:-

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X5 2006 3.0d M57N
GA6HP26Z Tranny
180,000km