The Dymo 450 Label Printer specifications state compatibility with Windows PC and Mac computers - but makes no mention of other types of computer such as iPad...:
https://www.dymo.com/label-makers-printers/labelwriter-label-printers/dymo-labelwriter-450-direct-thermal-label-printer/SAP_1752264.html
Your label printer requires device-driver software - this being installed on the host PC/Mac. For modern PCs and Mac, the driver-installation process is largely automatic and occurs during the initial device connection.
iOS/iPadOS has no means by which device-specific device drivers can be dowloaded and installed. Instead, device-drivers are installed on iPhone/iPad by installing a manufacturer-provided App - that, where available, is obtained from the Apple App Store. Dymo has not released a compatible App for iOS/iPadOS that adds necessary support for their label printers.
Unless you can identify a third-party App for your iPad, your existing label printer simply won't be usable with iPad.