If the machine's screen displays 'Sorry, maintenance required', it indicates the machine is attempting to connect to bill validator, but receiving an error condition.
This could be due to a few reasons. In order of most likelihood, here is what we ought to check:
Cash box is full or improperly seated
Open the machine and remove the validator's cash box.
If there is a full stack of bills, empty the cash box.
In either case, then reinsert the cash box by pushing it back in fully until you feel it lock into place.
The validator should make a mechanical startup sound. If the validator does not make a startup sound, and the screen doesn't return to 'Buy Bitcoin', check further steps below.
Validator requires a power cycle
The validator may need a power cycle to re-establish communication with the machine's computer.
Power off the tablet by pressing once and quickly releasing the tablet's power button. Once it's on a fully black screen, unplug the machine from wall power for 15 seconds. Then, plug back in.
If the 'maintenance required' screen returns upon boot, proceed to the next step.
An obstruction exists in the validators' bill path
It's possible a foreign object such as a coin or paperclip has entered the bill path of the validator, or there is a note jam.
Open the vault door, then remove the bottom vault plate with the hex screwdriver that accompanied the machine. Once removed, the front of the validator is exposed. Gently lift up on the green handle to release the bottom half of the validator and carefully pull towards you to remove.
On the underside of this validator portion are two flaps that expose the bill paths. Hold down on the two green buttons on both sides near the mouth and gently lift on the flap to expose the mouth's bill path. Check for obstructions.
Close the mouth's bill path, ensuring it's firmly in place. Then open the transport's bill path by pressing on the green tab towards the back of the validator's underside. Check for obstructions.
Place the validator portion back into the vault, along the rails on the underside of the cash box, until it's firmly in place. Reboot the machine by pressing once and quickly releasing the tablet's power button, await the machine to go fully black, then press once again.
If the 'maintenance required' screen returns, proceed to the next step.
Wiring and cabling
Check that the cables underneath the machine's tablet are fully pushed in, and that there are no visible breaks or cuts as they travel towards the vault.
Was the machine moved prior to experiencing the 'maintenance required' screen? Was the bill validator removed from the vault in the process of mounting it in the new location? If so, the cabling within the vault could be loose, disconnected, or damaged if not handled carefully. Carefully the full validator as before to check if this is the case.
If the cabling appears damaged, or the screen continues, create a support ticket and we'll gladly assist.