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Is this affecting all texts sent to different contacts or a particular contact ?
I'm thinking if it's a particular contact then you may have inadvertently added the number to the phones blocking facility or the contact has.
Might be worth checking your account settings in your myvodafone.
If your sending ling texts or ones with photos in then the normal text would change to a MMS which costs to use and some accounts need provisioning.
Can you try a soft reboot by turning the phone off and on as this may just be a glitch and refreshing the network connection may help.
And check your text messaging centre number.
" Message centre number - +447785016005 "
If you can as a process of elimination try your sim card in another phone.
And check your mast status via Vodafone status-checker.
Live Chat or the Vodafone Social Media Teams via Contact-us-for-account-specific-queries can check your account.
Current Phone > Samsung Note 10+ 5G _256Gb > Model: SM-N976B.
Samsung One Ui 2.1 / Android 10.
Samsung Gear s3 Frontier Watch.
Samsung Galaxy Buds.
Thanks very much, this is helpful! Gonna have to get them to check my account though... Thanks again!