[8] Iwannis met with the Caliph Marwan II at Harran, and presented him with fifty camels laden with gifts, for which he was awarded a decree that authorised him to perform his patriarchal duties.
[9][10] The patriarch's troubles began in 746/747 on the issue of the succession of the highly coveted diocese of Tur Abdin after the death of its incumbent bishop Athanasius of Nunib.
[10][12] Opposition to Iwannis grew as the monks of the monastery of Saint Matthew supported Athanasius' right as archbishop to designate candidates to empty suffragan sees, and accused Iwannis of ordaining bishops for eastern dioceses (within the former Sasanian Empire) without the approval of Paul, archbishop of Tikrit, and thus against church canons.
[10][12] The dispute between Iwannis and Athanasius Sandalaya thus came to a head, and the latter resorted to an appeal to the Caliph Marwan by accusing the patriarch of having extorted 150,000 dinars from the archdiocese of Tikrit and the eastern dioceses, and of simony.
[16][17] The Caliph Marwan detained Iwannis at his monastery at Harran, and forbade him from leaving until he had paid 12,000 dinars and made peace with Athanasius.
[16][18] The battle marked the end of Marwan's rule as he found no support in Syria, and fled to Egypt, where he was killed in August 750.