Creating a catch-all issue for reports of "Invalid Match Key Parameters" for AddToCart and ViewContent Events. We are investigating more but the advice to date has been

“​… this problem seems to affect only ip_address and user_agent parameters for two specific events. As we’re not seeing this issue widespread across the platform and this problem is affecting only a small amount of events from this Pixel, the problem may be due to users having ad-ons to their browser to avoid submitting information to websites. I recommend reviewing Pixel Settings and the code on the website itself to check for any issue. If there are no issues in the parameters requested on the website and the code is correct, please run a test using the test event tool. The admins may go ahead and click Mark as Resolved to see if the issue persists.”

Some initial problem-solving steps

• check your pixel is connected
• its likely related to browser extensions blocking user agent and IP address
• enable debug logging and see if you are getting any obviously errors

Reports

• 3 Warnings in Pixel #1771
• https://wordpress.org/support/topic/server-sending-invalid-match-key-parameters-for-viewcategory-event/#post-13433313
• https://wordpress.org/support/topic/server-sending-invalid-match-key-parameters-issue/
• https://wordpress.org/support/topic/server-sending-invalid-match-key-parameters-for-addtocart-event-8/
• https://wordpress.org/support/topic/issue-server-sending-invalid-match-key-parameters/
• https://wordpress.org/support/topic/server-sending-invalid-match-key-parameters-for-viewcategory-event-2/