i want to add a contact on my PC who is not in my contact list, when i try to send a message inviting that person i get "

It is possible that this person has set their privacy to not being discoverable in Teams:

https://support.microsoft.com/en-au/office/manage-privacy-settings-in-microsoft-teams-free-20847062-fcdc-42db-977a-386f964d8834

If this is the case, then the other available option is to send the invite link to their email address or phone SMS.

https://support.microsoft.com/en-gb/office/invite-contacts-to-microsoft-teams-free-e8792a52-dfde-4fe5-90a5-4aaca0274c51#id0ebf=desktop

Hi lawrence, thank you for posting here in the Microsoft community, to help you add a contact on your PC (especially for Microsoft Teams or Skype), here’s what you can do.

First, Open Teams or Skype on your PC then Click “Chat” or “Contacts” then Click “New Chat” or “Add Contact” then enter the full email address of the person (preferably their Microsoft 365 or Teams email), If it says, “The contact doesn’t look right”, try, Using only the email address, not phone or Skype ID, Confirm the email is linked to a Microsoft account and Try adding them via Outlook Contacts first, then sync to Teams.

If you're using Skype for Business, it may not support adding external contacts unless federation is enabled, if you're using Microsoft Teams (personal), it may not allow adding work/school accounts and try adding the contact via Outlook People and see if it syncs to Teams.

Is the contact you're trying to add using a personal Microsoft account or a work/school Teams account? This helps narrow down compatibility issues.

I hope this helps you out, let me know how it goes.

Chard