This usually happens when you have installed an eSIM but the activation hasn’t completed as you are not yet in Japan.
It can also happen when you are in Japan but the eSIM is still registering on the network.
Please do not worry. The eSIM is fully installed, even if it displays “activating” or “activation failure.”. Please do not delete the eSIM.
The activation process will finish when you reach Japan and/or you connect to the Docomo network. Here are some screenshots on what you may see for reference: 
Once you reach Japan and/or the device is within the network coverage area, the eSIM should activate successfully, and as long as you have set it as the default SIM for Cellular/Mobile data, you should be able to start using it!
If you have any questions, please feel free to contact our support team, and we’ll be happy to help!