There are various reasons why you can't be able to add images or videos to the album. The first reason is that you don't have any access to the internet or your internet connection is not stable. Using Coupled requires an internet connection. You need to make sure you're connected to the internet or have a stable connection to add images and videos.
The second reason is that you don't have enough space on your Coupled cloud storage. Free users get up to 0.5GB of cloud storage. This will upgrade your storage up to 16GB. To add more storage, you can buy the premium bundle.