Connecting to a private teams group

I am trying to link various excel files that are all located on private team groups and getting various errors

I trying using connect excel files and obtained the access is forbidden message

Further research suggesting using link via a web page and then Sharepoint folder which i have also tried

Connecting via a sharepoint page and via a web page gives another message

The service returned an invalid token,  Please contact your IT adminstator if this issue persists.  x-ms-request-id

The process i am following as detailed below

For both sharepoint folder and web page,  i open teams and then opened the sharepoint site and copied the link so reads https://companyname.sharepoint.com/teams/sitename

I then click Ok

I then get the sign in window which if i connect via a sharepoint folder does not give me a organisation account, but i cannot sign in and I get the error message above.

Firstly, which method is the best method to use or should i be using another route to connect?

Secondly, if one of these methods is correct is this a permissions issue?

Any other hints and tips greatly appreciated

Many thanks