Button Not Working on iPad in Interactive PDF Exported from InDesign

As everyone else noted, interactive PDF is no longer the format to pursue if you want interactive publications from InDesign usable on many platforms. I would suggest switching to Fixed-Layout EPUB output. It has almost all the benefits of the old interactive PDFs plus pretty consistent features across devices. In InDesign go to File > Export and set the output format to EPUB (Fixed Layout).

The only real drawback is that neither Windows nor Android have built-in FXL (Fixed-Layout) viewers; they require the user to install an FXL-capable ebook app like Kindle.

What did you program the button to do?

Multi-state buttons don't work on tablets and smart phones and in any case interctivity on PDFs is limited.

Interactive PDFs generated by InDesign are best viewed using Adobe Acrobat.

Some 3rd party readers don't hold all the modules for interactive pdfs - which are essentially dumbed down PDF readers offered by Apple, Goodnotes, Samsung, Chrome, Foxit Reader etc. don't all comply with all features of a PDF. 

If you want an interactive PDF to work on all devices you may need to reduce your interactive or change methods etc. - or insist everyone have Acrobat to view the PDF.

An alterative is to Publish Online which might work for you either.