Hello Michaela! Looking at your question I believe you have done everything correctly. In WAM Studio Dashboard, the app should have been shown as "Upload Complete" and then as "Pending Testing".
Please confirm that the validation instance was launched from the WAM Player AMI, in the same VPC and Public Subnet as the WAM Studio packaging instance and that it has the same role attached to it (AmazonWamAppPackaging that has the managed policy AmazonWorkSpacesApplicationManagerAdminAccess attached to it)
If you still have issues I suggest to open a new support case with us and to provide the logs from WAM Studio (C:\Program Files\Amazon\WAM Studio\wamstudio.log) and WAM Player (File and Options - Log tab - choose View Log, along with the instance ID's for each instance.
References: https://docs.aws.amazon.com/wam/latest/adminguide/application_packaging.html#cant_get_apps https://docs.aws.amazon.com/wam/latest/adminguide/iam.html#app_package_role https://docs.aws.amazon.com/wam/latest/adminguide/application_log_files.html
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