Dolphin cannot work without mbstring extension

Hello,

Since yesterday, I have the message 

""""""""""""""

mbstring extension not installed. Warning! Dolphin cannot work without mbstring extension. 
Please go to the 
Dolphin Troubleshooter 
and solve the problem.

""""""""""""""

Knowing that I did not work on my website, and that this morning I tried to update 7.1 - 7.1.1 but the message is always here!
Have you a solution plz?

If its dedi or vps you have to install it,

If its centos try this

yum install php-mbstring

Otherwise try contacting your host.

Thank you,

it was during the transfer from the server,

the hosting provider had not yet installed mbstring

now, it's ok,