An unlock is required for protected wallet functions when the access token that you are using does not have any spending limits applied to the token. 


You may either call the unlock endpoint found here: https://www.bitgo.com/api/v2/#unlock, or you can simply recreate a new token that you have applied spending limits to. Applying spending limits to the token will surpass the requirement for calling the unlock endpoint when you wish to spend and the OTP requirement for spending.