Got error 'invalid UTF-8 string at offset 1' from regexp - regex

Question

I need help, I have tried to find the solution but until now all I have found is stuff related to regex but I think the problem might be in another place.
I have a project locally (Windows 10 --> Xampp Latest version [Apache & Mysql], I use CodeIgniter as Framework, I developed a function which searches in my database using REGEXP (I use query builder)
It works fine and everything. Here I searched for saltarín <-- Note the accent on the letter i
So now that it works I have decided to update the online website but as soon as I was testing the online project I noticed an error jumps when I search something with accented characters or in this case the letter ñ which also works locally.
I checked my database configurations, in database.php I have dbcollat set to utf8_spanish_ci and my online database and tables are set to utf8_spanish_ci too, I think this must be a server configuration but I don't have an idea of what it really could be
In case you need it this is the piece of code which uses regexp
$this->db->where("lower(secret_colum_name) REGEXP", $this->secret_hehe);
Thanks a lot for your time, I really appreciate your help.
EDIT: I forgot to mention I'm using hostinger to host my website

Answer 1

It's me again. It was just as I suspected it was something about the server, After some hours of research I found out that my server didn't have the same extensions and configurations, you can use php -m command to find out your local extensions so you can then enable them on your remote server which in my case I had to do by c-panel but your case could be different.
I also changed my php version in the remote server and I'm not really sure about the next thing but it might have helped.
I had a setter defined in my model which did the next thing
$this->my_var = strtolower($my_var);
I removed strtolower and after all the steps previously mentioned I reloaded my site and now it works