LED reverse bulb type and size

[Enigmasdream]

Sorry to open an old post, but have just changed the drl in my t6 2018 from h4 (will change back for mot) to led.
Hated the orange look and replaced with twenty20 382 led bulbs.
All good.
However, thought I could do the same for the reversing light (torch more like) as can't see anything with the standard bulb.
But the led bulb won't fit in the bayonet fitting.
Am I being dumb?.....yes
Can someone please help me and point in the right direction so I can take off the whole light unit again but this time with success!!
Thanks

 

[Paynewright]

Pictures might help show the problem

 

[ginkster]

The reversing bulb can be a H21W or a P21W. Guessing yours is an H21W variant which is why your P21W (382) won’t fit.