Hello Artur Gawrych**,**
Good day! Thank you for reaching out to Microsoft community.
I understand that you are experiencing an issue with users being able to sign up for Microsoft 365 product trials even though you have disabled the option "Let users start trials on behalf of your organization" on your tenant.
Based on the context provided, it appears that the issue you are experiencing is not a bug, but rather expected behavior. Even though you have unchecked the "Let users start trials on behalf of your organization" option, users may still be able to sign up for Microsoft 365 product trials.
The context indicates that this is a setting that controls whether users can access the Office Store and start trials on behalf of the organization.
By unchecking this option, you are preventing users from accessing the Office Store and starting trials on your organization's behalf.
However, it does not necessarily prevent users from signing up for trials on their own.
To fully prevent users from signing up for trials, you may need to explore additional settings or configurations within your Microsoft 365 tenant. Unfortunately, the provided context does not offer information on any other settings that may need to be adjusted.
To know more about these configurations, I would suggest contacting with Microsoft support.
If you are interested to do so, please let me know, I will share whole process.
Therefore, based on the given information, it seems that the behavior you are observing is the expected outcome of unchecking the "Let users start trials on behalf of your organization" option, but there may be additional steps required to completely prevent users from signing up for trials.
I hope this helps. Let me know if you have any further questions or concerns.
Please understand that our initial response may not always resolve the issue immediately. However, with your help and more detailed information, we can work together to find a solution.
Thanks for choosing the MS community.
Looking forward to your response and have a great day ahead!!
Sincerely
S M Nazmun Nur | Microsoft Community Moderator