LimeSurvey Version 5.3.6+220321

Hi, 
I'm trying to upload paricipants to the survey drom csv and I get the following error:

"400: Bad Request
The CSRF token could not be verified. 
The request could not be understood by the server due to malformed syntax. Please do not repeat the request without modifications."

It seems that is related to the number of participants I'm trying to upload (45000) as when I'm trying less records (e.g. 2500) there are no errors.
Maybe this is relevant: I've recently upgraded from LS version 2.52 to 5.3.6, (I didnt had those problem on the previous version). The server is also different (for advanced php version)
Any idea where and what are the settings that needs to be changed?

Thanks!
 

Just to update that I saw in similar posts that this has something to do with the php configuration. I've tried changing "post_max_size" , "upload_max_filesize" and "max_input_vars" in php.ini but no change.
If anyone has experienced something similar appreciate if you could guide me how to solve it

From what to what did you change these values? Because my guess would also that these variables are responsible for this, as you have no problems to upload 2500 records, but run into trouble with higher numbers.

Have a try where the limit is and if that limit goes up when you increase these PHP variables. My guess would be the "max_input_vars".

Thanks, I'll try to update this field again.

I've increased the "max_input_vars" number but still no change.
Are there any other settings that might cause that?

To what did you increase it? 10.000? Where does it max out now?

What about 100.000?

I've increased it to 100,000

Well, then I am done with my tips.

I think this has something to do with the Timeout and also the memory settings in the PHP ini file I was having similar issues with uploads as well as reporting and exports for an extremely large file so I set
memory_limit to an excessive 10240M and max_execution_time to 1200 and this seemed to resolve the issue for me.

I had a participants file of 320K names and emails along with 200K responses and this also fixed the invitation sending timeouts as well.

Great , It seems that it works.
Many thanks!