Summoned by the Pope

Giotto 

When the elderly Pope summoned him [Francis] one last time, he had refused. This was something no child of the Church would ever do. But he did. He flat out refused.

Firstly, there had been the argument about the gentle creatures and their places in heaven. The Church had been adamant that animals did not have souls, and therefore his services with the small creatures, were considered to be no more than an empty bluff - a charade - a performance - a novelty. Francis was ordered to address the mortals only.

The Holy Father, added to this, had placed stipulations, and confinements upon the activity of his Brotherhood.

-Gabriel Brunsdon, AZLANDER: NEVER ENDINGS: Second Chances

"In 1209, Francis of Assisi led his first eleven followers to Rome to seek permission from Pope Innocent III to found a new religious order which was ultimately granted....

After several days, the pope agreed to admit the group informally, adding that when God increased the group in grace and number, they could return for an official admittance. The group was tonsured. This was important in part because it recognized Church authority and protected his followers from possible accusations of heresy, as had happened to the Waldensians decades earlier. Though Pope Innocent initially had his doubts, following a dream in which he saw Francis holding up the Basilica of St. John Lateran (the cathedral of Rome, thus the 'home church' of all Christendom), he decided to endorse Francis's order. This occurred, according to tradition, on 16 April 1210, and constituted the official founding of the Franciscan Order."