Tal Vez accepts indicative and subjunctive?

Question

Hello, in one of the lessons I read Tal Vez accepts both indicative and subjunctive, but when I included the indicative in my answer to the following question, it was marked wrong.

Tal vez ________ una gala benéfica para los niños pobres.

There might have been a charity gala for poor children.(HINT: Conjugate "haber" in El Imperfecto de Subjuntivo)hubohabríahubierahubiese

Could you please explain?

Silvia Piriz · Accepted Answer

Hola Devin P.
Tal vez can take either the indicative or the subjunctive depending on the level of certainty: with the indicative (tal vez hubo…) the speaker sees the event as more likely, while with the subjunctive (tal vez hubiera/hubiese…) it sounds more doubtful or hypothetical.
In everyday Spanish both are correct, but in this exercise the hint specifically asked for the imperfect subjunctive of haber, so only hubiera or hubiese are accepted as correct answers.
Saludos
Silvia