Regarding the PDP Authentication Error on your iPhone, please try the following steps:

1. Please turn off your other SIM cards/eSIMs. If it is a physical SIM card, please take it out of your phone.

2. Delete/Remove the Sakura Mobile APN profile.

(Go to Settings---> General---> VPN & Data Management---> Select Sakura Mobile profile---> Remove).

3. RESTART the phone/device.

4. After the restart, please reinstall the APN profile on your device.

***Please note that you MUST install the APN profile by using "Safari", not other browsers.
APN settings: https://www.sakuramobile.jp/apn-settings_longtermsimcard/

5. If the SIM/eSIM works, you can insert your physical home country SIM card and/or turn it back on.

6. If Steps 1-5 above do not work, please try deleting the current APN profile you have downloaded.

7. Get connected to a WiFi connection instead of your other SIM connection(s) - if applicable; please connect to a WiFi connection such as a home WiFi, public WiFi, etc.
 
8. Perform a Network Reset:
Old iOS version: Go to Settings---> General---> Reset---> Reset Network Settings
Latest iOS version: Go to Settings---> General---> Transfer or Reset iPhone---> Reset---> Reset Network Settings
※Please rest assured that a Network Reset will only erase APN settings, which can be reinstalled at any time. 
This will not affect your SIM or any other data stored on your phone.
 
9. After the reset, please reinstall the APN profile on your device.
***Please note that you MUST install the APN profile by using "Safari", not other browsers.
APN settings: https://www.sakuramobile.jp/apn-settings_longtermsimcard/

If the above does not resolve the issue, please contact us, as it may have been caused by other reasons.