It appears the fee free passage may only be for the 60 day negotiating period. Based on wording of the MOU reported in several places (the source for the below was Fox) the terms of passage beyond the 60 days are to be negotiated by Oman and Iran (with input from other Gulf states).
"5. Upon the signing of this MOU, the Islamic Republic of Iran will make arrangements using its best efforts for the safe passage of commercial vessels with
no charge for 60 days only from the Persian Gulf to the Sea of Oman and vice versa. The traffic of commercial vessels will immediately start and, considering the needs for removing the technical and military obstacles and demining by the Islamic Republic of Iran, will be instated within 30 days.
The Islamic Republic of Iran will conduct dialogue with the Sultanate of Oman to define the future administration and maritime services in the Strait of Hormuz in discussion with other Persian Gulf littoral states in line with the applicable
international law and the sovereign rights of coastal states of the Strait of Hormuz."