Hello,
I am experiencing some anomaly on the web UI.
I would like to add a new URL to my library and nothing happens.
No changes in the list of folder.

I hope these details help your investigation:

- In Chrome DevTools I can see failed API calls to the "items" function:

Request headers:
======================
POST /users/=== PROBABLY MY USER_ID ===/items?format=json HTTP/1.1
Host: api.zotero.org
Connection: keep-alive
Content-Length: 288
sec-ch-ua: =========== I REMOVED IT
Zotero-API-Key: =========== I REMOVED IT
sec-ch-ua-mobile: ?0
User-Agent: ============== I REMOVED IT
Content-Type: application/json
Accept: */*
Origin: https://www.zotero.org
Sec-Fetch-Site: same-site
Sec-Fetch-Mode: cors
Sec-Fetch-Dest: empty
Referer: https://www.zotero.org/
Accept-Encoding: gzip, deflate, br
Accept-Language: en-US,en;q=0.9,hu;q=0.8

Payload:
=========

'[{"itemType":"webpage","url":"https://www.zotero.org/support/dev/start","title":"dev:start [Zotero Documentation]","abstractNote":"Zotero is a free, easy-to-use tool to help you collect, organize, cite, and share research.","accessDate":"2021-05-18T19:02:07Z","collections":["== I REMOVED =="]}]

Response headers:
======================

HTTP/1.1 500 Internal Server Error
Date: Tue, 18 May 2021 19:02:07 GMT
Server: Apache/2.4.46 ()
Strict-Transport-Security: max-age=31536000; includeSubDomains; preload
Access-Control-Allow-Origin: *
Access-Control-Allow-Methods: HEAD, GET, POST, PUT, PATCH, DELETE
Access-Control-Allow-Headers: Authorization, Content-Type, If-Match, If-None-Match, If-Modified-Since-Version, If-Unmodified-Since-Version, Zotero-API-Key, Zotero-API-Version, Zotero-Write-Token
Access-Control-Expose-Headers: Backoff, ETag, Last-Modified-Version, Link, Retry-After, Total-Results, Zotero-API-Version
Zotero-API-Version: 3
Zotero-Schema-Version: 3
Content-Length: 17
Connection: close
Content-Type: text/html; charset=UTF-8