Azea Augustama was taken into custody in Miami and booked on three felony charges -- two counts of issuing written threats to commit a mass shooting and one count of threatening to kill or do bodily harm.

He was ordered held on $3 million bond at a court hearing.

According to an affidavit, obtained by TMZ, Azea's membership at Miami's Boxr gym got yanked earlier this month after he had a heated argument with someone.

Then, on Tuesday, Azea had the police escort him back into the gym to retrieve the possessions he had left behind, but they had disappeared.

Azea later took to social media to vent his anger over his missing belongings ... making "threats to kill or do bodily harm with a firearm," the affidavit states.

He went so far as to tag the gym in a few of his threatening Instagram posts, which also included a deposit receipt for an AK-47. He later deleted the receipt.

Police were notified about the threats and tracked Azea to the pawn shop where he had originally put down the $150 deposit for the weapon.