Warning Message : call_user_func_array()

Situation
The client is facing website down issue.

Reasons
Generally, this is the following reason that causes this error :
PHP version is not updated but WordPress version is updated or vice versa it is a compatibility issue, because of which when PHP function is called that may be an outdated function(old PHP version) or the function that is not present.

Communication to Client
Tell the client that this error is caused due to the above-mentioned reason. In order to fix the issue, our development team has to check the WordPress version and troubleshoot other compatibility issues (like PHP version conflicts with wp version). This needs time to fix, it will be very tough for non-tech savvy to fix this, therefore, requires the technical expertise and we will provide it for you.

Prerequisite
Client's Hosting URL.
Client's Hosting Credentials (Username and Password)
Importantly: Verify the credentials then and there over the phone or via chat.

Sometimes it becomes so tough to know the Client's hosting, therefore always ask for Hosting URL.
To check the website information Go to https://www.whois.com/

ETA
5 to 6 hours

Always confirm the time frame with the developers.

References
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Updated on: 30/07/2018