Hey there
Most likely network dependant.
1. Do you have a spend limit on your contract? If so are you over this limit?
2. Have you turned off Premium Rate Text messaging? For example Vodafone allow you to do that in your MyVodafone app settings or online.
One of the above is the most likely reason why you've not been able to send them.
I am not employed by Samsung nor do I receive any remuneration as a Samsung Members Star.
My device is an S25 Ultra.