After Adding few Custom Fields for publishing with searchable option , I noticed that the search by Custom Fields doesn't work :
 - After clicking on "Search", it doesn't search according to the Custom Fields
 - After clicking on "Search", the selected Custom Fields (checkbox) is not selected anymore
 - I have repeated the test with a Drop-down field and same issue

I did the same test with a free theme and it works :
 - After clicking on "Search", it can search according to the Custom Fields
 - After clicking on "Search", the selected Custom Fields (checkbox) is still selected

I have installed a lot lot mb-themes plugins and I am going to install them on the free theme because that problem might be the plugins and not Zara theme ...

For information, I have just disable all plugins, and the search by custom fields still doesn't work ... then the problem might come from Zara theme ...

For information, I have just activate Bender theme instead of Zara (with all plugins deactivated) and then received the Error Messages below ...
After installing Zara Theme, we might not be able to go backward and install any other theme instead ...
Anyway, I am going to test all these on a new installation ...

( ! ) Warning: urldecode() expects parameter 1 to be string, array given in C:\wamp\www\zara\oc-includes\osclass\classes\Rewrite.php on line 192
Call Stack
#   Time   Memory   Function   Location
1   0.0110   397288   {main}( )   ...\index.php:0
2   0.0120   474600   require_once( 'C:\wamp\www\zara\oc-load.php' )   ...\index.php:23
3   0.0980   7103744   Rewrite->init( )   ...\oc-load.php:271
4   0.0980   7103952   Rewrite->extractParams( )   ...\Rewrite.php:166
5   0.0980   7105792   urldecode ( )   ...\Rewrite.php:192

( ! ) Warning: urldecode() expects parameter 1 to be string, array given in C:\wamp\www\zara\oc-includes\osclass\classes\Rewrite.php on line 192
Call Stack
#   Time   Memory   Function   Location
1   0.0110   397288   {main}( )   ...\index.php:0
2   0.0120   474600   require_once( 'C:\wamp\www\zara\oc-load.php' )   ...\index.php:23
3   0.0980   7103744   Rewrite->init( )   ...\oc-load.php:271
4   0.0980   7103952   Rewrite->extractParams( )   ...\Rewrite.php:166
5   0.1000   7107480   urldecode ( )   ...\Rewrite.php:192

( ! ) Warning: Cannot modify header information - headers already sent by (output started at C:\wamp\www\zara\oc-includes\osclass\utils.php:1738) in C:\wamp\www\zara\oc-includes\osclass\utils.php on line 1741
Call Stack
#   Time   Memory   Function   Location
1   0.0110   397288   {main}( )   ...\index.php:0
2   0.1590   8876160   CWebSearch->doModel( )   ...\index.php:102
3   0.1590   8876296   BaseModel->redirectTo( )   ...\search.php:175
4   0.1590   8876296   osc_redirect_to( )   ...\BaseModel.php:113
5   0.1590   8860072   header ( )   ...\utils.php:1741

@Chris
Error reference to core, it seems to be problem with friendly URLs.
Please send us URL where we can reproduce issue with search.
We were not able to reproduce issue on our demo site:
https://zara.mb-themes.com/search/category,1/sOrder,dt_pub_date/iOrderType,desc/meta1,option+1/meta2,1

Hi frosticek,
I cannot launch and market my website because I don't have any list of cities and I have contacted a freelancer to modify the code to be able to post/edit/search cities as text field ... This freelancer is full during the next 2 weeks and can it later ...
Then, I am testing Zara and all plugins on Localhost with Wamp ...
Anyway, I will install that website on a server in few days or during the week-end at the latest (that website is a hobby) and will send you the URL ...

@Chris
Ok

I have replaced Wamp by Xampp and no more error messages after a search ...
The search by custom fields doesn't work with any themes including Bender ...
Localhost might be wrong too, need to test the custom fields on the server ...

@Chris
Ok, I am marking this as solved, it seems issue is not with theme.

Hi Frosticek,
You are right, that issue is solved ...
After installing Zara on Xampp Localhost instead of Wamp Localhost, then no more error messages ...
I am an Osclass beginner and have just noticed that when we enable Permalinks (Show More/Settings/Permalinks), then the search by Custom Fields work fine ...
Thank you for your support,
Chris

Welcome