Im not asking you to update the theme. Please update your plugin. If you have customize in your child theme then after updating all data will be safe but if you have customized in the core file of plugin then you will lost your all customized data.
Please check now. I have logged in to my account and i have enabled bank transfer to purchase sub pack and i have purchased a pack for $1 and now i can upload product. You can check that account which one is given to me.
I can understand you. But it would be great if you can update to the latest version. I think there is something wrong. You did lots of customization so it is complicated to find out the problem. In our side everything is working fine because we are using the latest one. You can check our demo- http://demo.wedevs.com/dokan. Child theme is a safe way to customize so customizing in core file its not good.
I have to discuss with our developer team about this. Please allow me some time. I will be back to you after the discussion with them.