Are you using the S1 app for the Port? 
The Arc is only compatible with the S2 (new) app.

You should have used the new app to set up the Arc, so you will need to use that version to update the Port.

When adding the Arc, did you set up a new system or add to the existing one?

Hi, I am using new app for the Port and cannot add a new component (Arc).  Do you mean I have to download S1 for the Port and S2(new app) for Arc?  Thanks.

No, you should be fine on S2. What error message do you get, or why can you not add the Arc? 

Hi nik9669a, yes I tried but not success adding to the existing system.  The app can’t find the new component.

Make sure you have the latest app update. There was one earlier this week. Then try to add the Arc again.

If all else fails, try doing a factory reset on the Arc.

Thanks Pools 3015, I did as you said many times but still not success to adding the Arc even I tried to remove all devices and add again.  The app only allows add one of them only, the other one always can not be found.

Can you describe your network?

There are a few things that Sonos does not recommend using within your network. Look here:

https://support.sonos.com/en-us/article/sonos-system-requirements

If you do not have any of those things within your network, you should try hardwiring the Arc to your router/network to see if that helps.

If all else fails, I suggest you give Sonos support a call so that they can investigate further. Thay have tools that can pinpoint issues with their products.

Thanks Pools3015, I finally fix the problem and I can put both devices into the app and work very fine.  My mistake is not reset the Arc to factory reset properly.