Jackson decided to invade Florida.

From The Battle of New Orleans: Andrew Jackson and America's First Military Victory by Robert V. Remini.  Page 20.

Now convinced that the British planned their invasion through Mobile with Pensacola as a base of operation, Jackson decided to pursue the retreating British marines and Indians and invade Florida. Such an action would disrupt British plans, punish the Spanish for violating their neutrality, and put an end to the Indian war in the south. Although he admitted in a letter to the new secretary of war, James Monroe, that “I act without the orders of the government,” still he said he felt “a confidence that I shall stand Justified to my government for having undertaken the expedition.”

But he needed additional troops for such an expedition. Fortunately, his friend General John Coffee started southward from West Tennessee with more than two thousand cavalry and even picked up several hundred more troops along the way. When he learned of Coffee’s approach and the size of his force, Jackson wheeled out of Mobile on October 25 to rendezvous with him. By the time the combined force reached Pensacola the American army comprised over 4,000 men, including 1,000 regulars and several hundred Choctaw and Chickasaw allies.