Filelink Thunderbird Add-On refuses the upload

I was asked to:

Rona

-> I can't do that as I can not login, can not change password . . . I can't do anything -> strange:

Today I tried to upload two files  . . . one succeeded the other one I had to do with dropbox.

Hello dear box.com support team,

Perhaps someone here can help me… but first, some information:
TB: 115.6.1 (64-Bit)
OS: Windows 10
Account Type: POP
Mailbox Provider (split): SMTP marec.de (own domain) / POP (Incoming server:) gmail.com
Storage Service (the one that is / isn’t working ;)): box (box.com)
AV: Windows Defender Firewall: Windows Defender (and Fritzbox)

On the subject: For many years, I have been using the Box (box.com) add-on with Filelink (from a certain attachment size). It has always worked great. However, for some time now, the upload always fails, I can no longer use Box (box.com) in conjunction with Thunderbird. There is no further error message, except that the “upload failed”.

I have already “uninstalled” and re-set up the service several times -> no improvement. If I try it e.g. 5 times with Box (box.com), it may work on the 5th try or already on the third try or only on the 7th try and sometimes not even then.

Since I have a lot and enough storage at Box, I am informed about the download time and frequency. Box (box.com) is simply the better solution. Although I also use Dropbox, out of necessity, I would like to use Box (box.com) again. Can anyone help me with this?

Thank you in advance for your help!

With best wishes,
Marko