If you are using the OptimizeMember and OptimizePress file downloads and you get this error when testing your downloads:
503: Basic File Downloads are NOT enabled yet. Please contact Support for assistance. If you are the site owner, please configure: optimizeMember -> Download Options -> Basic Download Restrictions.
The solution is to go to the OptimizeMember > Download Options > Basic Download Restrictions section and setup the download options there. You can setup individual download restrictions for each level or set the basic level and above
If you want unlimited downloads you can enter the information as shown in the screenshot below: