I'm getting a blank page or 500 Internal Server Error in any of MultiMerch or OpenCart areas
Blank screen issue can be caused by a number of reasons. First, make sure your server has error logging enabled and check your server's main error_log. It will have the exact error message specified – see the rest of this guide for a solution for the most common error messages. If you're still getting a white screen or if the error message isn't mentioned here, please contact us using the form below and specify your installation details and the error log message you are getting in the log file.

I'm getting a Fatal error: Class 'ControllerMultisellerBase' not found error
This is usually caused by an incomplete or broken vQmod installation. In most cases, it either means you haven't run the vQmod installation script after uploading vQmod files to your server or that your web server doesn't have write permissions on vQmod folders vqmod/ and vqmod/vqcache/. In some cases it can also happen if you're using an older version of vQmod – make sure you use the latest vQmod 2.5.x for OpenCart.

Please make sure you follow the vQmod installation guide that is available on vQmod's official GitHub page.

If you're absolutely sure your vQmod is installed and functioning correctly, but the error still persists, make sure you've uploaded MultiMerch vqmod xml files from the upload/vqmod/xml/ folder inside the MultiMerch archive to the vqmod/xml/ folder in your store.

I'm getting "Error: Table does not exist" database errors
Errors like "Notice: Error: Table 'ms_seller' doesn't exist. Error No: 1146" happen when MultiMerch database tables aren't created during setup, which usually means you haven't installed MultiMerch via Admin > Extensions > Modules > MultiMerch Digital Marketplace > [Install].

This is covered in our MultiMerch installation guide so please make sure you follow each of the steps described in the guide.

I'm getting a Fatal error: Cannot redeclare Loader::__get()
If this happens when you are installing the Journal2 theme per our guide, please rename the vqmod/xml/multimerch_core_oc2_loader_magic.xml file to multimerch_core_oc2_loader_magic.xml_ (add the underscore), proceed with the installation and then rename the file back.

If it happens with any other theme, simply remove the vqmod/xml/multimerch_core_oc2_loader_magic.xml file.

MultiMerch menu entry doesn't appear in my OpenCart administration area
In most cases, this is caused by a missing or incomplete vQmod installation. Make sure you install and configure vQmod correctly - this should solve the problem. Detailed vQmod installation guide is available on vQmod's official GitHub page.

This can also happen if you're using relative paths in your config.php and admin/config.php files. Please make sure you're using absolute paths in DIR variables.

MultiMerch entry doesn't appear in Admin > Extensions > Modules
Make sure you've copied MultiMerch files from inside the upload/ directory of the MultiMerch archive file to your OpenCart root. Copying the archive file itself will not work – you need to upload the files and folders that are found inside the upload/folder.

MultiMerch features don't appear in my front store
If you're sure that your vQmod is installed and working, this is caused by your custom theme. Please see our custom theme compatibility integration guide for MultiMerch for a step-by-step guide on making your custom theme work with MultiMerch.

I'm getting file upload errors or form submission errors ("Error occurred when submitting the form. Please contact the store owner for more information.")
File upload errors and form submission errors are caused by a number of reasons. First, check whether you have any errors in your OpenCart error log. By default, it's located in system/logs/error.txt or system/storage/logs/error.log. Starting with MultiMerch 7.1.3, you can also see the last 50 errors in Admin > MultiMerch > Debug.

If there are no errors in your log, you'll need to debug the issue. Open up the Network tab in Chrome Developer Tools (F12 > Network) and reload the page that causes the error. You will see some URLs in the list.

After the page has finished loading, click the button that causes the error with Network tab still open. A new request will appear in the list of URLs. Click this request to reveal the server response.

As you can see, here the actual error is Call to undefined function mb_strlen(), which appears because this PHP setup doesn't have mbsting extension enabled. Enabling it fixes the form submission error.

I'm getting allowed memory size errors or "Fatal error: Allowed memory size of 67108864 (or any other number) bytes exhausted"
This error means your PHP instance runs out of memory when trying to render the page and is usually caused by the memory limit defined in PHP configuration.

OpenCart sets the limit to 64 megabytes by default in its php.ini file. You can increase the maximum allowed memory amount PHP can use by adjusting the memory_limit variable in the php.ini file to, e.g. 128M:

memory_limit = 128M;

Alternatively, you can do this in .htaccess file directly:

php_value memory_limit 128M

"Notify seller via email" radio button doesn't get saved
It isn't supposed to. This setting is applied every time you're saving seller data and essentially means "notify seller about this particular data change". It defaults to "No" every time you reload the form again.

MultiMerch email notifications don't work
First, make sure that your mailserver is set up and configured correctly and that your OpenCart mail settings are right. If OpenCart emails don't get sent as well, it's an issue with your mail configuration.

If OpenCart emails are getting sent correctly, but MultiMerch order notification emails don't work, see the answer below and check your order statuses.

Orders aren't visible in MultiMerch seller area even though I see them in OpenCart. Order notification emails aren't being sent out by MultiMerch
Make sure your orders have a "Completed" status. Some OpenCart payment gateways place orders in a "Pending" status by default so you may need to change this in Admin > Extensions > Payments > [Edit]. MultiMerch doesn't treat pending orders as finished and therefore doesn't display them to sellers. When an order becomes "Completed", it will be visible to MultiMerch sellers.

If you still can't get completed orders to display in MultiMerch seller dashboard, make sure you have "Completed" enabled in the "Financial > Fund statuses" setting in MultiMerch configuration. Only the statuses enabled here will be treated as "Completed".

Vendors can't change the order status
There are two different order types in MultiMerch – orders and suborders.

MultiMerch doesn't cannot allow the vendor to change the "real" or "main" order status – the one used by OpenCart – because a single order may contain products from different vendors and changing its status to e.g. Completed would affect other vendor royalties.

Instead, MultiMerch allows vendors to change the status of their own part of the main order – we call this a suborder – through the "View Order" page in their accounts. Thus, the "real" or "main" order status that is used by OpenCart remains unchanged, but customers are still notified about a vendor changing the status of his part of the order.

Changing the "Product validation" setting doesn't seem to work
The product validation setting is applied to sellers during signup process so changing the global setting doesn't affect existing sellers. If you're changing the product validation setting globally, you'll also need to modify the existing individual seller accounts via Admin > MultiMerch > Sellers > [Edit] for the new value to get applied to them as well.

MultiMerch saves decimal prices incorrectly and uses , instead of . or vice versa
OpenCart stores currency separators for decimals and thousands in the main language file – MultiMerch merely uses them. Please make sure that decimal_point and thousand_point variables are set correctly in your main language file.

For the English language, the file is language/english/english.php and separators are configured as follows:

$_['decimal_point'] = '.';
$_['thousand_point'] = ',';

Vendor shipping fees are missing from order totals when using MultiMerch Shipping addon

OpenCart 1.x:
This is caused by OpenCart rewriting the database entry for MultiMerch Shipping totals module to its default Shipping totals module, which often happens if you install/modify/remove order totals modules in Admin > Extensions > Order Totals.

To fix this, you will need to rename the default order totals module record in the database into MultiMerch module. The following fields need to be present in the database:

Table: extension
Type: total
Code: ms_shipping (OpenCart rewrites this to "shipping")

Table: setting
Key: ms_shipping_status (OpenCart rewrites this to "shipping_status") 
Group: shipping
Value: 1

If the corresponding records exist in the database, you can update them to MultiMerch by running the following SQL queries:
UPDATE extension SET code = 'ms_shipping' WHERE code = 'shipping';
UPDATE setting SET key = 'ms_shipping_status' WHERE key = 'shipping_status';

OpenCart 2.x
This is caused by Subtotal and/or MultiMerch Shipping order total modules being disabled in Admin > Extensions > Order Totals.

To fix the issue, make sure you have Subtotal, MultiMerch Shipping and Total modules installed and enabled in this particular order ("sort order" field).

Seller, seller group and product tables are empty in the admin area. No sellers are displayed in the admin area even though I have successfully created a vendor account
When MultiMerch data tables are empty, they will have "No data avalable in table" message displayed. If a table looks empty and this message isn't present, this means there was an error generating it. The image below shows the difference.

In most cases, this happens because of the missing or inaccessible dataTables language file. To verify this, open up Console in Chrome Developer Tools (F12 > Console) or Firebug and reload the page. You will see the error that prevents the table from loading – either 403 Forbidden or 404 Not Found.

To fix this, make sure that the language file displayed in the error message exists in the dataTables language folderadmin\view\javascript\multimerch\datatables\lang\, is readable by the server and not blocked by .htaccess rules. If the file exists, but isn't accessible, you may need to contact your hosting provider to help you unblock it.