The refill filament may get loose or tangled due to improper installation. If you had the same issue, the following steps would help you avoid it.
Take the Bambu Lab Spool as an example. It has two parts, one has a raised locating point, and one not. The refill filament must fit in the locating point to install properly.
Twist the spool in the opposite direction to disassemble it. The part with the locating point is flat on the top, and its inner side has a groove that can be slid into.
The opposite part has no locating point, it is flat at the bottom. But its top has a buckle that can be slid into the groove to lock the spool.
There is a notch on the bottom of the paper spool, aim it to locating point, then push the filament to the spool. You will see no gaps between the filament and spool, and the filament cannot be twisted when it is properly installed.
Before locking the spool, make sure the opening side of the filament ties towards the side, in case it was covered by the top lid. If you already missed this step, you can also use scissors to cut the ties.
After that, push the second part in, then twist both parts in opposite directions. Once the spool is locked, you can see the notch and groove shown in the above photo.
You cannot check the lock status from the other side. Do not take off the filament ties before confirming it from the other side.
Put the filament into a clip or insert it into the holes on the side. After that, you can take off the four ties and enjoy your new filament.