Nanni was not a customer but an investor. Nanni and someone named Šumi-abum likely paid for Ea-nāṣir's transport dues, amounting to 36 talents of copper (over a metric ton, about 1080 kg). Those transport dues are translated as Dilmun tithes because it was a 10% impost on trade goods from Dilmun.

In this letter (see more here), Nanni states that Ea-nāṣir offended him, a shareholder / business partner, by acting inhospitably. More importantly, he did not produce on time, by request, nor with quality material a favorable return on investment.

At the end of the letter, Nanni says that Ea-nāṣir is to lose selection privileges in that he doesn't get to pick and choose what materials his investors received: "Be aware that from now on I will not accept bad copper from you. In my own courtyard, I will select and take (the ingots) myself."

So, Nanni (and company) are still going to utilize Ea-nāṣir for purchasing and importing copper, but Ea-nāṣir won't have the ability to pick and choose what his investors receive.