The "assert code 200" error is a common issue that occurs when using Cydia Impactor. This error typically appears when Cydia Impactor is unable to connect to the Apple Developer portal or when there's an issue with the device's UDID (Unique Device Identifier).
The free developer certificate you used to sign the app has expired.
Apple drastically limited the ability of free, non-paying developer accounts to sideload apps using older automated tools. Step-by-Step Fixes for Assert Code 200
Impactor hasn't been updated to match these new protocols.