1. Introduction
2. How to block a card?
3. How to unblock a card?
4. How to customize your own blockers? ( For Account Owners and Workspace managers)
5. Blocked cards' comments in the History log
1. Introduction
Blocking a card indicates a problem (blocker) preventing the card from progressing to the right on the board because it gets immobile. Once a card is blocked, it needs immediate attention to be resolved and get unblocked.
The blocked card's coloring turns red so it can stand out on the board and help you visualize problematic areas. The block reason is visible when you hover over the card. When you block the card, it becomes immobile and if you try to move it, you will be informed that you have to unblock the card in order to move it, and given the option to do so.
Note: If you open the card, the blocker icon is visualized at the upper left corner.
A blocked card cannot be moved to the next step in the process flow, but there is no restriction to move the card to a different swimlane in order to change its type or a priority.
Each card accumulates "blocked time" that is stored in the Metric tab of the respective card. 
2. How to block a card?
There are several ways to block a card:
Option 1: Open the card Context menu and select the Block icon. The "Block Card" panel opens (Img.1) and the system prompts you to select a blocker. You can use the dropdown menu and select the most relevant blocker. The menu provides a list of all blockers created for your team as well as the default Generic blocker.
Note: You cannot use the "Generic blocker" without adding a block reason comment and shortly explain why you are blocking the card.
Option 2: Open the card and go to the Settings menu in the upper right corner. Select the "Block" icon and use the same navigation as described above to proceed with the blocking.
Option 3:
Block a card using the Card Tokens panel on the Board Sidebar. There are two ways:
- Open the card token panel, select the blocker, and drag & drop it to the card.
The card will be instantly labeled with the color and the icon of the respective blocker token and will become immovable until its resolution. If you open the card, the blocker is visible in the upper left corner of the card. - Note: If you press CTRL + drag & drop the selected blocker to the card, the system opens the "Block card" panel, where you can provide additional comments relevant to the Blocker.
3. How to unblock a card or change the block reason?
To unblock a card, open the Card Context menu or the Card Setting menu and click the "Edit/Unblock" button.
You have two options:
- to unblock the card - just click the button and the card gets unblocked.
- to edit the block reason - there are situations in which you need to change the block reason without unblocking the card, especially if the problem is multi-layered. Click the Edit reason button and change it.
Note: You can unblock a card or change the block reason, directly from the Card Details. Open the card and right-click on the blocker icon at the top left card corner. This opens a new box and you can either edit the block reason from there or unblock the card. 
4. How to customize your own blockers? (for Workspace Manager and Account Owners)
Account Owners and Workspace Managers can customize the blockers that will be applied to the workflow process. Please, check the dedicated article to learn how to create your own blocker tokens.
Having your own list of the most commonly used blockers relevant to your unique scenario will sustain your process. Moreover, this will help you to group the blockers in clusters and analyze the type of reasons that block your projects most often and turn into bottlenecks.
5. Blocked cards' comments in the History log
The comment field is mandatory only when you select the Generic blocker.
Even though the comment field is not mandatory for the rest of the blockers, many users provide valuable information right there. When the card is unblocked, the free-form text will retain as an entry in the card History log. Users can refer back to it during retrospectives and team discussions on process improvements.
