If I run a discount for a bookstore where anyone can get a discount until the bookstore actually opens for sale, after which the signup period closes and anyone who got the discount can now use it. Is it ok to offer people to sign up for a discount code early while the business is not open for sale?

Ustadh AbdulAziz al-Haqqan

If you own it and fulfill all the requirements, then u can promise them sales and when the time for the actual transaction comes u sell them for the agreed price.