Problems connecting Sharepoint to our CRM system (Onlyoffice)

[Hen-ux]

Hello everyone,

We have been having problems establishing a connection between Sharepoint and our CRM system (Onlyoffice) for months.

The CRM system is cloud-based (https://www.onlyoffice.com).
The connection is intended to be used to store our backups from Onlyoffice directly in Sharepoint. But every time we try to connect, we get an error message:

We have entered the connection URL correctly, as well as the user name and password. The user is a global administrator. We have also entered all sorts of folder titles, but it still never works.

We have been in contact with both Onlyoffice and Microsoft support for months, but no one has a solution. According to Onlyoffice, the problem lies somewhere in a setting on our Sharepoint instance, as our CRM system can be connected to the Sharepoint instance of Onlyoffice itself. There are only problems with our instance.

So I am asking for advice here, can anyone help?

Thank you very much!
Hen