A problem with Nextcloud passman and Firefox

hello, I want to explain the problem in english.

I have install the app “passman” in Next Cloud and the Add on for firefox.

Now my problem is that a cant connect to the passman. I get the following popup: “Request has forbidden by Antivirus” - after I have disable that Kaspersky.
I get the following popup: JSON.parse:Unexpected character at line 1 column 1 of the JSON data.

Who can help me ? What must I do the solve the problems.

Firefox 59.02 + Nextcloud Passwords 1.5.0
Nextcloud 13.0.1