On some Android phones, both the Facebook and Instagram in-app browsers (as of today) behave incorrectly when the accept attribute is specified for an upload field within a promoted or linked landing page. The button therefore had no function. If you open the page in an external, normal browser outside of the Facebook app, everything is fine. This is annoying (especially since it has been reported for a long time), but it can be solved with a workaround.
The following JavaScript fix solves the problem and makes the buttons work again:
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