How do 64-characters ETH work? Is this valid vs. my 40-character address?

Short story: I am setting up ETH validator with a third party and I provided my ETH 1.0 withdrawal address. Let's call it 0x1234512345123451234512345123451234512345

As all of you are familiar with this is "0x" followed by 40 Hex characters. Problem is I received the instructions for deposit to the staking contract, and with the withdrawal credentials to be use are:

0x0100000000000000000000001234512345123451234512345123451234512345

Which is "0x" followed by "010000000000000000000000" (24 characters) followed by "1234512345123451234512345123451234512345" (the 40 characters I provided

I am nervous as I don't understand why there are 24 additional characters in front, and especially the "1" is second place.

Does this make any sense to anyone? It's a very reputable staking company (i.e. they set up validators and run them for you, on a non-custodial basis).