When you choose Export Design (ZIP), Flexitive will provide you with a single exported ZIP file, no matter how many sizes you choose to export. The folder containing all of your sizes will have the naming structure Design_Name.ad_server.time_stamp.zip and is referred to as the Parent Folder.
An example of the folder configuration for a Flexitive ZIP export is:
> Individual Sizes (e.g. Design_Name_300x250.zip) - These are the files you will need to upload > Images and Code for the Design
ZIP exports are prepared this way so that designs exported with multiple sizes are still exported as one file, making them far easier to manage.
When you upload your Flexitive project to your ad server, you will need to upload the individual sizes (e.g. Design_Name_300x250.zip), and not the Design_Name.ad_server.time_stamp.zip file. This means you will need to extract the individual sizes folders from the exported ZIP before you upload your project. This is the case even if you are only exporting 1 size of design from Flexitive.