Can't accept / decline meeting invitations on iPhone

I've seen this issue posted by others over the course of several years but have NEVER seen a solution that has worked! Whenever I receive a meeting invitation on my iPhone, I can open the .ics attachment in the e-mail and add it to my calendar but I am never given the option to accept or decline the meeting. I can however do this on my MacBook. Interestingly, as soon as I have accepted the meeting on the MacBook, the option becomes available to me on my iPhone so that I can then decline the meeting on my iPhone if I have previously accepted it on my MacBook.

This issue has been with me for a long time and causes all sorts of frustrations because people often chase me up to see why I haven't responded (usually because I don't have my MacBook to hand) or if I reply by e-mail to confirm acceptance, they assume I don't know how to accept the meeting and ask for me to simply click on "accept".

The meetings don't appear in my Calendar Inbox on my iPhone until I have accepted them on my Macbook, after which they go into the "Replied" section.

I would love it if someone would finally share a solution which works so that I (and countless others!) can finally overcome this frustration!

Thanks.