Question IAP test card shows "This product is not available in your country/region"

Hello everyone, I'm currently facing an issue with IAP testing:

My app has been submitted to the internal testing group, and my IAP product has been set up and published on Google Play Console. I've also added my own email to the list of testers.

When I enter the game, I successfully open the IAP process and the product information displayed is correct. However, I cannot click on the test card or test information card to perform a purchase test. I then noticed that there is a red text on each option stating "This product is not available in your country/region."

Please see the related screenshot (the interface is in Chinese, please forgive me, but the red text on the options states "This product is not available in your country/region"):





I would like to ask if there is any setting error in my Google Play Console backend that causes this situation?

Thank you in advance to anyone who may be able to help me with my question.