If you have trouble installing a key fob, first ensure that it is has not already been paired with the Somfy One / One +. To do this, go to the "System" menu, and verify that it is not listed.
Next, verify that the key fob is within radio range of the Somfy One / One +. To do this, try to install the key fob just a few yards from the Somfy One / One +. Go to the "System" menu, tap the "+" sign in the upper right corner, and follow the prompts.
Finally, make sure there is not a problem with the battery by restarting the operation using a brand new battery.