So verse 19-23 Paul continues his testimony. He explains he was not disobedient to God’s call and he preached repentance which is why the Jews seized him.

Acts 26

24 Now as he thus made his defense, Festus said with a loud voice, “Paul, you are beside yourself! Much learning is driving you mad!”

25 But he said, “I am not [e]mad, most noble Festus, but speak the words of truth and reason. 26 For the king, before whom I also speak freely, knows these things; for I am convinced that none of these things escapes his attention, since this thing was not done in a corner. 27 King Agrippa, do you believe the prophets? I know that you do believe.”

28 Then Agrippa said to Paul, “You almost persuade me to become a Christian.”
9 And Paul replied, “Whether in a short time or long, I wish to God that not only you, but also all who hear me today, might become such as I am, except for these chains.”

30 Then the king stood up, and [with him] the governor and Bernice, and those who were sitting with them; 31 and after they had gone out, they began saying to one another, “This man is not doing anything worthy of death or [even] of imprisonment.” 32 And Agrippa said to Festus, “This man could have been set free if he had not appealed to [e]Caesar (Emperor Nero).”

Notes: https://www.biblewise.com/bible_study/questions/paul-agrippa.php
From a grammatical standpoint, scholars aren’t exactly sure how to translate Agrippa’s response. Some choices include:
“In a little thou persuadest me a Christian to become.” (Interlinear Greek-English New Testament, Baker)
New American Standard — “In a short time you will persuade me to become a Christian.”
NRSV — “Are you so quickly persuading me to become a Christian?”
NIV — “Do you think that in such a short time you can persuade me to be a Christian?”

Paul then addressed Agrippa directly. He was certain that the king would know what he had been talking about, for the king knew the prophets. Paul asked the king, point blank, “Do you believe the prophets?” and answering for him, “I know you do.” This put Agrippa in an awkward situation. If he said, “yes,” that the prophets had, indeed, predicted a suffering Messiah and Paul was witnessing to that now, then he would basically be accepting the fundamental basis of Christianity. On the other hand, if he said, “no,” then his standing and influence with the Jewish authorities would suffer because he would be denying the veracity of the prophets.

Now something that has bothered me is Agrippa’s second statement.  Agrippa states if Paul had not appealed to Caesar he could have gone free. Well, Paul appealed to Caesar because they were trying to send him to Jerusalem for his trial, which would have resulted in his death.

The scripture does not say Paul was free to go, or that Paul did not have to stand trial. It seems like going to Caesar was the only way to get Festus out of Paul’s way. Felix had already let Paul rot in bondage for 2 years doing the Jews a favor, and Festus was on the same path.

For anyone thinking Paul was free to go until he appealed to Caesar, I give you Acts 25.

Acts 25
9 But Festus, wishing to do the Jews a favor, answered Paul, “[a]Are you willing to go up to Jerusalem and stand trial there in my presence [before the Jewish Sanhedrin] on these charges?” 10 Paul said, “I am standing before Caesar’s tribunal, where I ought to be tried. I have done nothing wrong to the Jews, as you also very well know. 11 Therefore, if I am guilty and have committed anything worthy of death, I do not try to escape death; but if there is nothing to the accusations which these men are bringing against me, no one can hand me over to them. I [b]appeal to Caesar (Emperor Nero).” 12 Then Festus, after conferring with [the men who formed] his council, answered, “You have appealed to Caesar; to Caesar you shall go.”