Add-ons may be supplied in the compressed ZIP format and need to be extracted (decompressed) before they can be imported into your Affinity app.
If the archive contains one file, the file is extracted to the same folder as the archive. If you're unsure of the file's name, tap the icon to the left of Select, and then tap Date to help identify it.
If the archive contains multiple files, they are extracted to a subfolder alongside and named after the archive.