iMac Retina 5K, 27-inch, 2017 won't boot after RAM upgrade to 64GB

Currently my iMac Retina 5K, 27-inch, 2017 has 4 x 8GB DDR4 (2400MHZ) OEM RAM installed.

I wanted to max out the RAM to the full 64GB allowed for my model, so I purchased 4 x 16GB DDR4 RAM (2400MHz) to replace the OEM RAM from the following link on Amazon.

https://www.amazon.co.uk/gp/product/B07YDR5MXK/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

But when I replace the OEM RAM with the 4 newly purchased RAM, my iMac won’t boot up (no Apple logo or chime sound) just stuck on a black screen when the power button is pressed. I've left it in this state for a few minutes as I understand it takes 30secs or so for the iMac to recognise the new RAM, but still nothing.

If I remove all the OEM RAM and install 1 of the newly purchased RAM sticks on its own, the machine boots up.  I’ve tested all 4 of the new RAM sticks individually and all 4 boot up the machine and are recognised.

I can then add a 2nd and 3rd newly purchased RAM stick and the iMac still boots up.  But once I add the 4th new RAM stick the iMac fails to boot and remains on a black screen.

If I then remove the 4th stick and put back 1 of the OEM sticks along side the 3 other newly purchased sticks the iMac boots up.

Is there a reason I can’t get my machine to power up using all 4 newly purchased RAM sticks? Or is there something I’m missing and need to do? Any help or suggestions would be welcome. Its as if any combination will work as long as its not trying to use the full 64GB size.

Combinations I have tried are:

1-New 16GB (Tried with all 4 sticks)

2-Empty

3-Empty

4-Empty

iMac Boots up

1-Empty

2-New 16GB

3-Empty

4-New 16GB

iMac Boots up

1-New 16GB

2-New 16GB

3-New 16GB

4-Empty

iMac Boots up

1-New 16GB

2-New 16GB

3-New 16GB

4-New 16GB

iMac FAILS to Boot up

1-New 16GB

2-New 16GB

3- Old 8GB

4- New 16GB

iMac Boots up