authentication errors when mailbox used in multiple locations

[mrccocking]

Hi 

We have a client with a microsoft 365 mailbox that is licensed with business basic and is used in a dental software to send reminders to patients, this email address is setup in several different locations as there are multiple dental practices the client owns, we seem to be getting authentiation issues, stating username or password incorrect in the dental software (the dental software uses Oauth to authenticate)

I have check for sign in issues and nothing seems to be logged in azure AD

does anyone have any idea what the issue maybe or what i can do to identify the issue. 

Thanks in advance

[#2]

@mrccocking 

Are you saying there is NO any logs recorded in User Logons?

[#3]

Hi, I see logons but they all seem to be successful, I don't see anything that would lead me to identify the issue