Struggling with dialogue box

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I’m working on making a dialogue box that’s simalar to undertale or deltarune. When an option is selected, the dialogue box flashes to the interface with the portrait and text for a couple frames, maybe a second, but then goes back to the menu interface, instead of it continuing the dialogue.

Note I’m making my own dialogue box, not using the dialogue box extension.

be precise in what is your issue. otherwise no one will ever help you