cannot send gmail from mail on my mac

I have a Macbook Air running el capitan 10.11.6

I have recently upgraded my gmail to gsuite, which entailed a new Google setup.

Having done this I can no longer send email from my Mac.

Every time I try to send it says 'unable to verify account name or password' when I enter the password; and if I go to Accounts to enter it, there is no password field.

I can receive email fine.

I have deleted and recreated the account - still doesn't work.

I have deleted the password entries in the keychain and recreated all email accounts from scratch - still doesn't work.

Any advice?