@Mark24 Did your VPP account token expire?, you can check this by browsing to the following
Organization > MDM
Under VPP accounts your accounts should be listed, and it should show the token expiry date. I would also check your push certificate expiry because if that expires before you renew it your in for a world of pain.
Ran into this issue yesterday. Since our VPP account has been migrated to Apple Business, we had to download a new VPP server token from the Apple Business portal at business.apple.com to resolve the issue.
Log in with your Apple ID, then navigate to Settings->Apps and Books and look for the Download button in the "My Server Tokens" section in the lower right-hand corner of the page. Once the token is downloaded, follow the normal VPP token upload process in the Meraki Dashboard and everything should return to normal.