The machine screen states that there is a document jam, but I can't find any document jammed in the machine.
Thank you

First of all, how old is the device? If it is less than 3 years it should still be covered by warranty, and you should contact Brother-Support to get free onsite service. Otherwise try the following:
If you can print, but copying results in a Paperjam-Error the paperjam is in the document-feeder(where you enter the originals to be scanned).
Try to copy from the flatbed scanner(glass). If it works the document-feeder is the issue.
The feeder has several sensors(plastic-latches) to detect paperjams. Open the topcover, find the latches in the paperpath and check if they are blocked by paper-rags or staples etc. Also lift the feeder (so you can see the flat-bed) and check the lower side of the feeder. Also check the part where the scanned paper comes out. Also check if all the latches are moveable and go back into their original position (they are held by a spring).
If you don't see any paper-rags etc. and the latches move, then it is a loose cable or defective electronics, in that case you should call a technician.

There are two reasons to report a jam.

One, the obvious reason, a jam. The other, is not so obvious. Its because the paper did not get to a sensor in the correct amount of time.

For example, you have the input source loaded. If the page does not make it into the printer, then the first sensor it is supposed to hit, will trigger a jam report because it knows that the paper is not on time.

A quick test is to write the word "one" on the top page of the stack. Send a print job. Look in the paper tray and see if the page is still in the tray. If it is, then you have a problem with the pick rollers. Clean them off and try it again.