Error replacing region content

[nikorn]

Pico CMS and Pico Content Editor installed with Composer on Apache 2 (Ubuntu 18.04).

After editing an editable area and pressing Save button a new result is not saved.
On screen error message is "error replacing region content".

Browser console error message is "Failed to load resource: the server responded with a status of 405 (Method Not Allowed)" or "POST ... Error 405 method not allowed"

Apache config

<Directory /var/www/>
    AllowOverride all
    Require all granted
</Directory>

Pico CMS config

PicoContentEditor:
    show: true          # show/hide the editor
    debug: true         # enable errors reporting

Editable content

<div data-editable data-name="pages-first-content" data-markdown markdown=1>
    Start page
</div><!--end editable-->

Ones more strings from Browser console

PicoContentEditor : SAVE 
Object
regions:
pages-first-content: {markdown: false, html: "<p>↵    Start Page 35564↵</p>"}
__proto__: Object
__proto__: Object