Sendinblue redirect

I included the Sendinblue Plugin to my WordPress Site which has the Avada Theme, so I found out, that the Plugin of Sendinblue has a few problems with some themes.
When I submit a Contactform formular to send it, I get this message:

{“status”:”success”,”msg”:{“successMsg”:””,”errorMsg”:””,”existMsg”:””,”invalidMsg”:””},”redirect”:””}

The only similair question I found was -> https://wordpress.org/support/topic/displays-plain-success-error-exist-messages-after-sending-form/ but there was no working solution.

Did somebody had the same issue before ?