Outgoing SMS from CH Sunrise to DE Telefónica network fails since 1.8.1

[leloup314]

Checklist

• I can reproduce the bug with the latest version given here.
• I made sure that there are no existing issues - open or closed - to which I could contribute my information.
• I made sure that there are no existing discussions - open or closed - to which I could contribute my information.
• I have read the FAQs inside the app (Menu -> About -> FAQs) and my problem isn't listed.
• I have taken the time to fill in all the required details. I understand that the bug report will be dismissed otherwise.
• This issue contains only one bug.
• I have read and understood the contribution guidelines.

Affected app version

Since 1.8.1, including 1.9.1

Affected Android/Custom ROM version

Android 16

Affected device model

Fairphone 6

How did you install the app?

Google Play Store

Steps to reproduce the bug

1. Use a Sunrise Switzerland eSIM.
2. Set Fossify Messages as the default SMS app.
3. Send an SMS to a German mobile number on the Telefónica network (tested with O2 and Blau.de).
4. The message appears to send, but the recipient does not receive it.

Expected behavior

The SMS should be delivered.

Actual behavior

The SMS is not delivered.

Screenshots/Screen recordings

No response

Additional information

Recipient numbers are correctly formatted as international +49... numbers.

Sunrise CH → O2 DE: 1.8.0 works, 1.8.1/1.9.1 fails
Sunrise CH → Blau.de/Telefónica DE: 1.8.0 works, 1.8.1/1.9.1 fails

An SMS reply sent directly from the Android notification/dropdown is delivered successfully, including when using the affected versions.

Version 1.8.1 through 1.9.1 were installed via Google Play automatic updates. Version 1.8.0 was installed from the official Fossify GitHub release APK to verifiy that it worked previously.