If you are seeing the message "🔒 Locked items require an upgrade on the next page" on the top, this means that if you enter an amount in a box that has a lock 🔒 next to it, you will need to upgrade your version of TurboTax.
In TurboTax Online, Box 028 is on the left side, under Box 048: Fees for services.
If you have Box 028 on the T4A slip, and you answered Yes to the question Does the income declared in Box 028 consist of fees collected for services you provided? you have what the CRA considers to be self-employment or business income. You will need to use TurboTax Self-Employed Online and TurboTax will ask additional questions to report the income as self-employment/business income. You only need to answer basic information, such as business name and address (can be your own), industry code, and fiscal period (Jan 01 to December 31).