PHP Fatal error in contact-form-7

What other plugins and theme do you use?

Hello,

I use Avada theme and other plug-in supportable with contact form 7 are listed below,
1) Akismet Anti-Spam
2) Flamingo
3) Multifile Upload Field for Contact Form 7

Note: For your information, this issue exist with contact form 7 and Flamingo and avada theme active.

Try switching to the default theme (Twenty Seventeen) and deactivating all other plugins. Also remove all custom coding if you have added.

This is related and I can confirm it, too:

https://www.ads-software.com/support/topic/undefined-function-plugin_basename/