Here is the information needed to pay for admission to the parks through August 25, 2023.
First, you must have an account on the government website ecitizen, with an email address and password.
Everyone who is in Kenya, in different capacities, should have this because it is needed to obtain the visa online. However, there are those who obtained their visas online with an agency, in which case they will need to create one.

If you can no longer remember your password and/or have not marked it, you can change it, the important thing is to have at least the original email address or to have provided your phone number and have it active, because you will get several OTPs. For some you will be able to choose the mail or phone option, for others it may come only on the mail.

Once you get into ecitizen, you will see in the categories the Kenya Wildlife Service (KWS) which is the agency that regulates the parks.
But you can only see it by choosing the "see all" option at the top of the list, otherwise they will only show you the main ones, among which KWS is not.

Once you enter you will be asked to register only in case you have registered more than 30 days before on ecitizen, otherwise it may be difficult to log in. In that case, however, there is a ploy, you have to change your password (again via OTP received) and so it will automatically recognize you as "new" and let you enter the parks payment system.

Once you are in, you have the option to choose whether you are a citizen/resident or a tourist, to enter a vehicle with its specifications and license plate, and a number of people. You can also pay for other people, but at once you can only do this if they are all citizens/residents or all tourists; if they are mixed, you will have to re-enter the site a second time.
Citizens/residents can pay by Mpesa service or by credit card.
Tourists can pay by credit card only, in dollars.

It would also be helpful to print out the payment receipts that will appear on the site and be downloadable, so that they can be presented along with the passengers' documents, upon entry.
And have a good safari...in spite of everything, because it is always worth it!