I've had this issue on another device. Phones are should be able to turn developer options off but I don't think it always works.
As a general rule I don't use them anymore because I sync with my square reader often for delivery payments.
Unfortunately if tapping to turn them off doesn't work, you may have to factory reset the phone to get the flag turned off that is blocking you.
Square support or more likely your mobile carrier might be able to provide more specific instructions.
