The single most useful early check is watching the Downloader progress bar the moment you hit go on the install. If it never moves off zero percent at all, the file isn't downloading in the first place, and that almost always means Apps from Unknown Sources is off under Developer Options, blocking the whole process silently instead of showing you any kind of visible error on screen. This is genuinely easy to miss, because nothing on the Firestick's interface actually tells you the download was blocked before it ever began.

An off permission stops the download cold before it even starts moving. An expired numeric code typed into Downloader pulls a dead or entirely wrong link instead, which fails partway through or grabs the wrong file altogether. Low storage space on an older Firestick model can let the download start and finish just fine but then fail specifically at the install step, since the file has nowhere left to unpack itself once it lands. Each of these three needs its own separate fix, so identify which one you're actually facing before changing any settings at random on your device.

1. 1Apps from Unknown Sources turned off blocks the download from starting
2. 2An expired or wrong Downloader code pulls a bad file
3. 3Low storage on the Firestick lets it download but not install

Start with the permission, since it's both the most common cause and the fastest to check on any Firestick model. If that's already turned on, move to the code next, since Downloader codes for pulling app files do change over time as file hosts rotate. Only after both of those check out clean should you look at storage space, since that cause is somewhat less common but still worth ruling out on older or smaller-capacity devices before you consider anything more drastic like a full factory reset of the whole unit.