Yes, this is a condition of your rental, unlock the chain lock for e-bikes (the code for the lock is in the name of the bike) from the parking stand and then lock the bike securely with the cable or chain lock at the end of your journey with the same code. Use it too when you are taking a break during your rental.
You should always lock a Moby bike when you are leaving it unattended as losing the bike will incur a penalty and makes you liable for the cost of the bike in case of a theft.
Note: Moby E-bikes have combination chain locks, the code for the combination is in the name of the bike you have rented.