This really isn't a "healthcare" question, but they didn't offer a category for pharmacy or veterinary
A licensed veterinarin in California.....
writes a valid prescription.....for a client
Client wants to fill said prescription via the internet, using a "fullfillment house" in Florida that does NOT have a pharmacist or license......
Can they?
Can who? The veterinarian's client is not breaking any laws by trying to fill a valid prescription. Whether some internet company in Florida might or might not be breaking the law by selling the item is their problem.