Could be a number of things...
Your bobbin may have run out of thread. You need to check that.
If there is still thread in it, then the needle may not be actually 'catching' the bobbin thread when it goes down to make each stitch. That can be caused by not having the proper length needle. That is, if the needle is too short, it won't go down far enough to reach the thread to catch it. So, check to be sure you have the correct size needle for your machine.
It also might be the wrong type of needle altogether. There are needles for woven fabric and different needles for knits. Sometimes using the wrong type can cause the problem you are having so you need to check that as well.
If the machine is not properly threaded and/or the tension is not set properly, the machine won't stitch correctly, so you need to double check that.
Try these things and see if any of them help.
Your bobbin may have run out of thread. You need to check that.
If there is still thread in it, then the needle may not be actually 'catching' the bobbin thread when it goes down to make each stitch. That can be caused by not having the proper length needle. That is, if the needle is too short, it won't go down far enough to reach the thread to catch it. So, check to be sure you have the correct size needle for your machine.
It also might be the wrong type of needle altogether. There are needles for woven fabric and different needles for knits. Sometimes using the wrong type can cause the problem you are having so you need to check that as well.
If the machine is not properly threaded and/or the tension is not set properly, the machine won't stitch correctly, so you need to double check that.
Try these things and see if any of them help.
