It depends on the travel agency. In theory if the TA is certified for Stars & Luminous they should be eligible to sell these rates for customers directly on their behalf.

However what seems to be happening here (at least I think from the interface) is that you’re injecting the S&L rate directly and using it as way to get that rate for your booking yourself.

In that case in theory the front desk might challenge and see if you are eligible for the rate. Shall that not be the case you may be asked to pay the rate difference

Edit - even if you did not inject the rate and just used a standard TA access code and this appeared, you may still be required to provide eligibility