Out of nowhere warning page saying that headers have already been sent and mismatch

Hi everyone,
in installed IP a few weeks ago but only yesterday started to use it. Everything was working out of the box and very smooth. I adapted the settings to my needs and everything was working fine.
I then logged out, closed my PC.
Today i went back to my IP URL where i want to log in and find this error:

Severity: Warning

Message: mysqli::real_connect(): Headers and client library minor version mismatch. Headers:50554 Library:50645

Filename: mysqli/mysqli_driver.php

Line Number: 203

I have read somewhere in this forum that - back from 2017 - this could be a small bug that can be solved by adding some header declaration on the index.php at its top.
I did this, but the warning still exists.

Then i read that i can deactivate the browser cache through the developer console, but even this dd not work. For me it is obvious that some IP or cache syncing is not working but as i have not changed anything on my server, i do not know where this warning can result from.

Anyone has a tip? Thnks in advance for your time!

Googleing for Headers and client library minor version mismatch. gave me this as first result:

Seems like its a problem with your PHP version which maybe is outdated or whatever. I cant even tell as your Infos about your System or anything else (which InvoicePlane version?) is not provided.

Please answer these questions:


  1. OS?
  2. PHP version?
  3. MySQL MariaDB version?
  4. InvoicePlane version?

But pretty sure this is related to the fact that you use a PHP version that was not compiled with the MySQL version you are using it.

Thanks a lot for your support.
The thing is that IP was working like a charm and on the next day it did not work anymore. So i checked my PHP version where IP is installed on and it was 7.3.2

With a htaccess file i downgraded to 7.2 and everthing is working fine again.

Thanks again for your support and time!

You are welcome!

InvoicePlane works perfectly on PHP 7.4, you just have to match all server-requirements.

My personal tip:
Use PLESK and everything will work out of the Box, from PHP 5.6 up to 7.4 as everything is perfectly preconfigurated.

(Tested on Debian & CentOS)

Because in the end you should not stick with a PHP version that will soon be outdated and not maintained anymore.

Official site and EVERYTHING anyway is hosted on a Plesk Server btw.