Separate the provider from the office
Plug one computer into the modem or the main router with a cable, if a jack exists. If that computer stays online while Wi-Fi devices fall off, stop rebooting the modem and look at wireless. If the wired computer dies too, the provider or the modem is the first call.
A second router plugged in “for more Wi-Fi” often creates two networks and a maze of addresses. Printers then appear and disappear depending on which network a laptop joined.
Buildings in the Kansas City metro
Brick, plaster, metal doors, and a router buried in a basement cabinet are enough to kill a back office. Adding another extender with its own network name makes the phone book of Wi-Fi names longer. It does not always add coverage.
Name the rooms that must work: the front desk, the room where calls happen, and the corner where the card reader sits. Coverage is a floor-plan problem.
What a useful fix looks like
One network name you control, a password that is not the default, and access points placed for the rooms you listed. Guest devices and payment terminals sometimes belong on a separate network, but only when that split is simple enough to explain.
Request Wi-Fi setup when the symptom is wireless. Request networking when wired jacks, switches, or the router itself are the failure.