HTC One M9 Status 7 when installing Android 6.0

I have rooted, unlocked and got TWRP on my HTC One M9 but have removed it all, it is now relocked and S-ON. TWRP is also gone.

When I try to install the new 6.0 update the installation gets aborted with status 7. I know this means it's detected that my phone has been modified but how do I fix it?

Thanks in advance.