Hi annabitanga,
Welcome to the Sony Community!
You can only use the Safari browser when downloading PlayMemories Camera Apps using a Mac computer. Since you said that you have done this and still can't sign in, I suggest installing the apps directly on the camera itself.
Connect your camera to the internet using Wi-Fi
- Select MENU → [Application] → [Application List] → [PlayMemories Camera Apps]
- Connect to the internet by selecting [Network Settings] → [Access Point Settings]
Install camera applications
- Select and install the desired camera application from the list displayed.
To update the camera apps, you need to remove the older version installed in the camera. You can remove it by MENU -> [Application] -> [Application Management] -> [Manage and Remove] on the camera. Once done, proceed with installing the latest version.
If my post answers your question, please mark it as "Accept as Solution". Thanks_Mitch