Upload API not available on this site

[adnus]

Hi everybody!
I have some trouble with uploading papers. If the paper size is greater than 5MB, the a javascript message pops up and says "Upload API not available on this site".
Anyway, the upload of papers <= 15MB is successful, if I ignore this javascript message.
What can we do? I checked carefully all options for nginx, php-fpm and php.ini.

Thanks for your help!
Jens

[adnus]

We found the solution. You have to add this option to hotcrp: $Opt["docstore"]

Regards
Jens