When you create or modify a bol in your EffectConnect account, you have the option to turn 'in-house stock' on or off.
When in-house stock is activated, then bol will maintain that stock value after every stock update. When this setting is disabled, then bol will deduct the stock value which is forwarded with the stock which is still in the orders that are not sent yet.
You can see this more or less as an internal reservation system. So if you have for example 2 open orders in your bol sales account, bol will deduct the stock of this product, until the orders are shipped, if this setting is disabled. When EffectConnect sends a stock update, while these 2 orders are still open, bol itself will deduct the received stock by 2 pieces.
You can activate this setting in your bol channel. Go to 'channels > channel manager', edit your bol channel, and change the settings here.
Please note that this feature is only available when your bol channel is connected via the Channel Manager. To know if your channel is connected via the Channel Manager, read this article.
Please keep in mind that it can take a while before the changes are visible in your bol account. There is a new stock synchronization needed. To read more about the synchronization times, you can read this article.