Being unable to edit the quotation tab from will happen from time to time when you are selected on the client list, but not the sales advice tab.

When you view an item (a client), you will not be able to edit the quotation because you are not selected on any of the Sales Advice items (from the sales advice tab).

Quite simply, to overcome this issue you will need to navigate to the 'Sales Advice' tab on the side, and then click edit on one of the available sales advice items (or create a new item):

Select the Sales Advice tab (after selecting the client),
Then select the sales advice item from the list
Select edit on the bottom right
The quotation tab will now be available

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