If you want to proceed with setting up your older device, let me know:

This is a certificate error. Apple revoked older app signatures.

This involves downloading an unsigned IPA file (an iOS application archive) of an old WhatsApp version and side-loading it onto the device using PC software.

You may see an error message stating that your version of WhatsApp has "expired" and is no longer supported. This is not a bug. It's an intentional server-side block implemented by WhatsApp to phase out legacy versions. Even if you have the correct old version installed, the app may fail to connect to WhatsApp's servers, rendering it unusable for sending or receiving messages.