Hi, welcome to the forum

1st, make sure that your "company" matches. The Company in the DD has no space, the Company in column A has a space before the number.

To pull out the items related to a specific company, try this ARRAY formula in C2, copied down...
=IFERROR(INDEX('Contract items'!$B:$B,SMALL(IF('Contract items'!$A$2:$A$13=$B$2,ROW('Contract items'!$A$2:$A$13)),ROWS($A$1:A1))),"")
...confirmed by pressing CTRL+SHIFT+ENTER to activate the array, not just ENTER. You will know the array is active when you see curly braces { } appear around your formula. If you do not CTRL+SHIFT+ENTER you will get an error or a clearly incorrect answer. Press F2 on that cell and try again.