Nextcloud Talk cannot upload/share images to chat

I’m trying to share a picture via the Nextcloud Talk application on my Android 13 phone (Nextcloud Talk v. 15.1.2), but I’m not able to upload the picture to the given conversation (chat). I am also unable to share a photo from the Nextcloud Android app (v. 3.24.1) to a specific Nextcloud Talk conversation.
In both cases, the uploading stops at about 25% and ends with the error message “Failure”.
I tried it on another Android 12 phone and it doesn’t work either.
Cannot upload images more than 1 MB.

Sharing and uploading photos to Talk chat works correctly via the browser’s web interface.

I am using the SNAP version of Nextcloud 25.0.3.

What should I try?