How do I sign my pet into the vet?

You need to travel to the Vet along with you Pet. Then you can sign it in at the machine.

The pet is on the lot with me.

there should be a flashing machine in the vet that you can sign you pet in

If it is not sick you can't sign it up for anything but a general checkup or to be Neutered/Spayed.

Yes I know but none of the options are clickable

Yes I know but all the options are grey

I came here looking for answers to the same problem, lol. 

@Eclectic_Althea, just so I understand what you are seeing in the game:

The pet is at the vet's with you

The pet is sick with something

You tried to click on the electronic registering stand and the options are grayed out so you can't click on options.

If that is your case, are there any vets at the clinic when you go?

Are other Sims (ones you can't control) able to check in and get their pet seen by a vet?

Do you play with any Mods or Custom Content (CC)? 🤔

Hello. I traveled with my pet to the vet. (it's a vet I own if that makes a difference), but when I get there and I click on the kiosk to sign in, it only gives me the option to Disallow new customers or allow new customers. 

how do I get my animals spayed at my vet? 

@leachs27 If I'm understanding your question correctly, and unless this has changed, a couple of years ago I learned this the hard way (after my pet and vet almost died of exhaustion with my vet trying to cure her own pet at the clinic she owned)... If your vet owns the clinic she/he cannot cure her/his own pet at heir own/owned clinic! The vet will need to take their pet to another clinic that they don't own to get treated!

Now I almost always just have my vets carry around wellness treats (which they can make at their own clinic/vet equipment or purchase at another clinic) and have them feed this treat to their own pet as soon as they act sick at home. Depending on the illness, most of the time this will work. Otherwise, you will need to have a 2nd clinic in your game somewhere (it can be in the same 'world/town' or another 'world/town') that your vet can take their own animals to for treatment.