Hi @abdulmoiz222 and thanks for reaching out!
I’ve seen “Scan Engine Error: The signature on the request to start a scan is invalid” where a clear/purge of any caches on your site (including the Object Cache) fixed it. It’s certainly worth trying that first if you’re using a caching plugin.
Some specific plugin conflicts can also cause this message. Those can be diagnosed by disabling your other plugins one-by-one until the Wordfence scan starts working again. In other cases, the customer disabled the conflicting plugin permanently, but that doesn’t mean there isn’t an allowlist or other configurable solution where both plugins can run together.
If you don’t have a conflict and have cleared caches with no luck, you can send a diagnostic to wftest @ wordfence . com directly from the link at the top of the Wordfence > Tools > Diagnostics page. Then click on “Send Report by Email”. Please add your forum username where indicated and respond here after you have sent it.
NOTE: It should look as follows – Screenshot of Tools > Diagnostic > Send by Email
Thanks,
Peter.
