As you can see here:
http://www.open-spf.org/SPF_Record_Syntax/
The “+” symbol is used by default.
So both spf expressions are correct and equivalent.
The other thing that I suspect is that you are not configuring the correct DNS server.
In the domain registry you set the DNS server for that domain and then you configure that server.
If at the domain registrar webpage you have not set your HESTIA machine as the DNS server… then, the world won’t see the changes.
Otherwise anyone could set a DNS server for gmail.com and mess with people’s emails.
Please follow the guide I provided step by step and you will have everything working.