There are several reasons why the first layer of filament does not adhere properly to the bed.

Too fast Printing: The printing of the first layer should be done slow and controlled to attach well to the base. The parameter to modify to solve this problem is the “First Layer Speed”.

Bed temperature: If the bed is cold enough, the filament may get cold and not stick. This is solved by increasing the temmperatura of the bed to the recommended in the technical tab of the filament.

Change printing base: If your printer does not have a hotbed or base, you will need to purchase solutions such as glass crystals to increase adherence, or use a layer of adhesive.

Calibrate the height of the Nozzle: The idea is to reduce the distance between the bed and the nozzle. The most reliable in these cases is to level the printer again.