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Can you perform a soft reboot by turning the phone Off and On. This would help to re establish a fresh network connection. Also try choosing another network in the phones connection settings and then re choose Vodafone UK.
Take a look in your myvodafone to ensure no bars have somehow been toggled on that can affect texting.
If your sending long texts or ones with pictures in then this is classed as a MMS which isn't free and costs to send and a person needs a 3G data connection. Also some people need to contact Vodafone customer services to have this provisioned on their account to be able to use the MMS messages service.
Also as a process of elimination can you try your sim card in another phone. This is to help rule out the phone or sim card that maybe having issues.
Is this affecting texts to everyone or a particular contact ?
If a contact then check your phone for any blocking facility and ask the contact to do the same.
If it's everyone then check your messaging centre number.
Text messaging should be ready to go as soon as your phone’s connected. If it doesn’t work straight away, there are a few settings you can check:
• Message centre number - +447785016005
• Message format - this should be set to text
Some help links that go though self help troubleshooting tips and to check your masts via the Vodafone Status Checker.
As there is no account access assistance via the Vodafone Forum anymore you may need to contact customer services via 191 or Live Chat.
The Vodafone Social Media Teams via Contact-us-for-account-specific-queries have account access too.
I wish you all the best with this situation.
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.