You are possibly running an old version of PubGuru Header Bidding.
Step 1: Log into tools.monetizemore.com > MonetizeMore Header Bidding> Configurations
Step 2: Open the PubGuru Header Bidding feature and find the relevant configuration
Step 3: Uncheck the “Beta” box, and publish. This will run the most stable version.
Step 4: If for any reason you have to keep “Beta” checked, upgrade the configuration version to a newer one.
Check https://dash.pubguru.com/pghb-versions for information on the different PubGuru Header Bidding versions.
Step 5: Save and publish
Step 6: Re-run a debug test after 10-15mins
If you still encounter the error after upgrading, please report this to our support team with this notification title in the subject line and they’ll help you troubleshoot the issue.