You need to set your MMS APN to get group texts and picture texts working.
Find your values on your carrier website (each and every one is different) or maybe it will be listed here: World Wide Mobile Phone Settings
On the phone go to Settings> cellular + SIM> SIM settings> toggle "Manual Internet APN" to ON
Use the values needed by tapping "edit MMS APN" then inputting the values into the fields and selecting "save"
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