For Rent/Cats & Dogs: Can't treat pet on residential rental lot

The easiest thing to do is feed your dog a Wellness Treat. Wellness Treats cure all pet illnesses in my experience. You can buy them from the vending machine (Dr. Magi-Heal's Medical Vend-o-matic) at the Brindleton Pawspital. 

I don't have For Rent, so I can't test your problem myself, but it seems like the obvious solution would be to transfer some funds to your business.

I'd rather not go all the way to brindleton just to get wellness treats, and you can't transfer funds into a rental house. The revenue is transferred directly to the household funds.

I guess it is what it is.

You could try adding the vending machine to a community lot in your own world. I don't know whether it will work on other community lots, or only on veterinary lots. 

You could also try making the Wellness Ttreats yourself on Dr. Magi-Heal's Medicine Craft-o-Matic or on Dr. Budget-Bandage's Medicine Craftidink. The Wellness treat  requires level 5 Veterinarian skill.

@OmegaGamer123456 as @Sketch793 mentions the Wellness Treats work and also save time at the vets office itself, you mentioned it takes a long time there so instead of a vet's appointment you can just cut that part out and get the wellness treats from the machine to treat a pet without an examination. It's much quicker and once you've been there and bought a big supply of them you don't have to return. All my pet owner Sims carry a supply of Wellness Treats in their personal inventory.

If you add a vending machine at home it needs to be stocked manually by having your Sim create the treats. Or you can buy some again at the vet's office then take them to your new vending machine to stock it.

If you want a quick way to get some funds I usually get a collecting hobby like fishing, harvesting and collecting. Adding a few plants to harvest can be a real money spinner.

Money isn't an issue in my household, don't get me wrong. I actually prefer to use the exam table for the experience of it. It's just a shame I can't because of this darn bug.

Okay, okay, slow down a moment! I don't run a business at all. I use the vet table to treat my own pet. I don't wanna own a vet clinic, nor do I want to move my tenants out of the guest house as that defeats the entire point of my lot being a residential rental. The issue is that the game thinks a residential rental has a business funds account when it doesn't. There's really no solution for it that doesn't involve not using the exam table at home while still renting out my guest house.

@OmegaGamer123456You asked about that point in your first post and I'm agreeing, yes if you wanted to run a vet's office it would need to be on a different lot.

For bugs, we have a dedicated bug section here:
https://answers.ea.com/t5/Bug-Reports/bd-p/The-Sims-4-Bugs
If you'd like to just select New Topic there and fill in a bug template. Following this you may find that this is by design or it may be something that can be addressed. I haven't run into it on a regular residential lot. I am able to build vet skill on my residential rental lot but they don't have a sick pet currently to test it. I can make vet treats though and I've just opened my game to check that, she's creating treats with no problems.
If you can take images of the message you're seeing in your game to add to a bug report it would be helpful.

But for any sick pets in the meantime, the Wellness Treats are a quick solution you should be able to craft those if you don't want to go and purchase them.

If you play on PC there's also the option of looking for any mods to help. There's a mod section here with advice on using mods safely as well as giving the opportunity to ask questions.
https://answers.ea.com/t5/Mods-Custom-Content/ct-p/the-sims-4-mods-en

@OmegaGamer123456   Hi!  Please believe me when I say that I understand your frustration here.  However, the rental properties are considered a part of the owned business system.  So, what @simsplayer818 mentioned actually could be what is causing the issue.

I don't know if this would be considered a bug though.  The game was not designed to accommodate more than one business on a lot.  If anything, I would think the fact that sims can offer vet services on a rental lot might be a bug. That is something for the Sims team to decide.  I'm sure they will see this thread and investigate further.

Whatever the case, I think the best option to cure the pet is to give wellness treats as @Sketch793 and @simsplayer818 have mentioned.  If you don't want to go to a vet clinic to buy them or have your sim make them and you don't mind using cheats, you could use the bb.showhiddenobjects cheat and then search for "wellness treat" in BuildBuy.  You may also want to filter by the Cats & Dogs pack to find it more quickly.

I'm glad you guys are all trying to give advice here, but I'm not trying to run a vet business or offer vet services. I'm just trying to treat my own dog on my own lot so I don't have to go to a vet clinic. It shouldn't require "business funds" unless it's on a vet clinic lot type.