There are many reasons why the chart doesn't work. A first step is always to check if the designer is supported.
See Which designers are supported?

Some things to check/try if you chart does not import.

  1. Check if the chart is split into multiple parts. Not uncommon for charts with multiple panels or charts where you can choose components. If one pdf contains multiple charts try splitting the pdf and importing them separately.
  2. Check if any of the pages not containing chart pages contain something that that could be mistaken for a chart. A mockup with gridlines or an extra page with an alphabet. Remove these pages or remove all pages except for the chart and the thread list and try again.
  3. Clear the app cache. Restart the app and try again. (Sometimes the Android OS will interfere with the import process)
  4. Close all other apps and connect the charger and try again. (Same reason as number 3)