Is my action of increasing the profit margin and adding an extra amount to the invoices for the purchase and shipping of vegetables and fruits for my relative, without his knowledge or prior agreement, permissible (halal) or forbidden (haram)?

It is forbidden for you to add a profit margin and another sum for shipping and packaging without an agreement with the employer, because this is deception and treachery. Allah Almighty said: "O you who have believed, do not betray Allah and the Messenger or betray your trusts while you know [the consequence]." And the Messenger of Allah, peace and blessings be upon him, said: "Whoever deceives us is not of us."

However, it is permissible for you to take a fee for your work if you inform the employer and he consents to it. Otherwise, you must return everything you took without his knowledge, due to his, peace and blessings be upon him, saying: "The wealth of a person is not lawful except with his willing consent."