Renewed certificate and now Owntracks gives error

My NAS certificate was due for renewal, so I did that. All is installed fine, Hass works OK on it etc. Only Owntracks (Android) stopped working giving me this error: “Trust anchor for certification path not found”

How do I make it to trust the new certificate? Without reconfiguring stuff, neither in the Owntracks app, nor on the Hass side (API key, Owntracks integration entry)…