Visit the webstore, once you have selected the resource you would like, select "Add to Basket" button. If prompted to login make sure you login to your FiveM/CFX.Re Account. After purchase visit your keymaster for the download. (Note: It can take up to 10-15 minutes to appear in your keymaster)
If you want to contact support or contact Trase the best place to do so is through the offical Trase.Dev discord.