Not sure about replacements beyond return to Amazon and reorder… But. It might just be a blessing in disguise for you.
The adhesive they are shipped with is WEAK. I had several of my motion detectors crash and burn when the adhesive failed. Caused a false alarm.
You might be better off going to the Big Box store and grabbing some 3M double sided clear adhesive (that’s what I used and it will hold a screaming gorilla to the wall) or Command Strips. You will only need 1 pack as you cut them to fit.