you could try these steps
1 delete the app
2 switch off phone
3 restart phone
4 deleting all of the “magic link” login emails you have in your email account from Monzo previously
5 reload app
6 enter your email address as supplied to Monzo originally
7 wait for email magic link to be sent , don’t try again as this will upset the process - wait a good ten minutes
8 check junk mail folder if it hasn’t arrived
if that doesnt work help@monzo.com