Praise be to Allah.
It is well known in Islam that when buying gold for currency, the exchange should take place in the same sitting where the transaction is agreed upon, because the Prophet (peace and blessings of Allah be upon him) said: “Gold for gold, silver for silver, like for like, same for same, hand to hand… If it is an exchange of one of these things for another, then sell as you like, so long as it is hand to hand.”
Narrated by Muslim, 1578.
I think that buying gold via the internet is not a transaction that is conducted hand to hand, because you are sending the money to them then they send that gold to you after a while. If that is the case, then buying and selling in this manner is haraam, and it is haraam for you to bring customers to this company, because Allah says (interpretation of the meaning):
“but do not help one another in sin and transgression” [al-Maa'idah 5:2]
But if the money and goods are exchanged immediately in one sitting, then it is permissible for you to tell people about them and to bring customers to this company, and to receive payment for that.
We ask Allah to make our provision halal. May Allah send blessings and peace upon our Prophet Muhammad and his family and companions.