Microsoft Outlook pop up issues

Hi all, 

Facing an issue when sending a .ics calendar file via a Power Automate flow to users who fill in an MS Form. The email sends, but the attached .ics file, when opened, brings up the following Microsoft Oultook pop-up:

Clicking "Open as New" displays another pop-up to say "Operation failed" and clicking "Import" opens the calendar, but doesn't open for any particular date. 

Usually, when I send a similar .ics file attachment, users simply open the attachment and click to Accept etc, but this is no longer happening.

Any help on how to block the pop-up and have the regular meeting window pop-up instead to accept, decline, save & close etc (below):

Thanks