Is there an error code in the manual that matches the beep code?
If not, then I would suspect anything that has changed between the time it worked and the time it did not. In this case, that would be the wiring between motor and controller, anywhere between them, including at the entrance of or inside the hubmotor axle, but most commonly at the connection point.
If it is corroded, then there may be insufficient or no connection on any of the contacts. There may also be corrosion in any other exposed connector that sees the same environmental conditions that caused that corrosion, though it's less likely those are a problem unless they were handled or worked with between the time it worked and the time it didn't. Corrosion in a connector often also means corrosion between the wires going into it and the back of the contacts of the connector, sometimes breaking the wire.
If the hubmotor wheel was removed or manipulated, wires at the axle exit can be damaged if not careful, by pulling or bending or pinching, and it may not have any external sign of the damage. In this event you can use a multimeter to test for correct signals at the motor/controller connector(s) as long as those have pins accessible without disconnecting them. (they must be connected to do the test).
WIth the bike turned on and the wheel offground (upside down bike, for instance), you can set the multimeter on 20VDC, and put it's black lead on the thin black hall sensor wire. Put it's red lead to the red hall wire, it should read about 5v (a little less, usually). If it does, then use the red lead to the green hall wire, and manually very slowly rotate the wheel backwards (if it's a geared hubmotor it wont' give signals the other way). You should see the voltage change from somewhere around 0v to somewhere around 5v, repeatedly, as you turn the wheel. Move the red lead to the yellow hall, and then the blue one, repeating the test on each one. If any of those do not give those expected results, post what you do get and we'll go from there.
BTW, I don't really understand what the two attached pictures are intended to show us, as they dont' appear to show anything that you are posting about as a potential problem. I see a picture of a shock mount and chain and sprocket, and another picture of a battery and it's discharge connector and wiring, and the wires for the charge port. I can't tell if the sprocket is on a motor or a pedal gearbox. Do you have this bike?
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If so, it has a hubmotor in the wheel, so the chain sprocket there must be for the pedal drivetrain, and so not relevant to the problem you're seeing (and neither would anything else I can see in the images).
I recommend posting good clear well lit (direct sunlight is best) closeup pictures of the specific parts of the bike that are relevant to the things you are having a problem with, or those that are things that have been changed or altered between the time it worked and the time it didn't (like the wires between motor and controller, along their entire length, including the connectors) or with known problems (like the corrosion described), etc.
