My enterprise Teams can't add customer personal Teams id.

Just to clarify, your enterprise account is registered in China, right?

What about these personal accounts, are they Chinese users?

Dear Eric Yang,

To ensure I understand your request correctly and to support you as effectively as possible, I need more specific information from you:

Could you share a screenshot as the image below (go to Microsoft Teams admin center > External collaboration > External access)?

When you try to add each other, what exact issue message appears? Please provide a screenshot if possible.

How are you adding the user: by email address, phone number, or Teams username?

Is the customer using Microsoft Teams Free/personal with a personal Microsoft account, or Microsoft 365 through another organization?

Does the issue affect all personal Teams users or only this specific customer?

Can either of you communicate with other external or personal Teams accounts?

Does the same issue occur in the Teams desktop app, web app, and mobile app?

When did the issue begin, and has communication between these two accounts ever worked before?

Your provided information will help me assist you more promptly and efficiently.