Mirza Aqa Jan was induced to lay an independent claim to divine inspiration.

And so they [the CBs] secretly established communication with him and encouraged him to rebel. As previously mentioned, having deceived him, the Covenant-breakers instructed and trained him, fed his ego and on the strength of his eminent position as the recorder of the verses of revelation received by Bahá'u'lláh, induced him to lay an independent claim to divine inspiration. Their purpose, of course, was provocation-to create chaos in the hope that it would lead to a full-scale rebellion against the Faith.

The foolish Mirza Aqa Jan then spent a great deal of time preparing letters containing a description of the dream he had concocted, in which he claimed to have been admitted into the presence of Bahá'u'lláh and through divine revelation and inspiration to have received and written down words expressing God's indignation and outrage. It was these messages that he had planned to send to various devoted believers. In one case he claimed that he had received directly from heaven a Tablet inscribed in green ink commanding him to rescue the Faith from the clutches of the infidels. The writings contained the same accusations and insults hurled at 'Abdu'l-Bahá by the Covenant-breakers, except in much harsher and more venomous language.

He had planned to hand over these papers to the Covenant-breakers on the day of the anticipated revolt. Their intention was to copy the contents in the hand of Mirza Majdu'd-Din, who had been Bahá'u'lláh's amanuensis during the latter part of His life, and then disseminate them among the friends. That is why, on this day, he was carrying the papers under his 'aba, fastened around his waist.

(Memories of Nine Years in Akka by Youness Khan Afroukhteh, Oxford: George Ronald, 1952/2003)

https://bahai-library.com/afroukhteh_nine_years_akka