What (Windows version or macOS version) are you trying to run this on?
Adobe Photoshop CS3 is officially considered "dead," as its activation servers were permanently shut down in 2017. Because these servers no longer exist, a standard authorization code cannot be generated or verified through the software's original activation process. Status of Activation authorization code for photoshop cs3
If you have a serial number but the "Authorization Code" field is blank or won't accept input: What (Windows version or macOS version) are you
Even if you attempt to use the offline activation method, the underlying issue remains—the servers required to accept the authorization code are permanently down. Modern Alternatives to CS3 Status of Activation If you have a serial
Adobe Photoshop CS3 is officially considered "end-of-life," and obtaining an authorization code is no longer possible through traditional activation methods because Adobe shut down the CS3 activation servers in 2017 Current Status of CS3 Authorization Retired Servers
This specific version did not require internet activation or an authorization code.