Hello there,
Thanks for contacting us. I hope you are doing well.
Please make sure, you have permission to attach the files. You can check permissions at Support > Settings > Rich Text Editor > Agent/Registered Users/Guest > Allow attachments > Enable > Save the changes.
Also, make sure you have added the file extension at Support > Settings > File Attachment > Allowed file extensions(comma separated) > Add the extension if not > Save the changes.
I hope this will fix the issue. If this does not resolve the issue then try to create from admin panel(backend) of your site, if you are able to upload the file then it might be conflict with another plugin.
?You can troubleshoot this yourself by disabling all plugins and activating them one by one. This way you will find the plugin causing the conflict. The same applies to the theme, if you didn’t find conflict with any plugin, try changing the theme and if the issue is gone, it is a conflict with your theme. Please note, that the theme should not be changed directly on the live server, sometimes you may lose settings. I recommend you create a staging site and then check the issue on it.
Thank you.
